Genuine Gurus are rare these days, so this question shouldn’t arise, but for what its worth, these are some insights by Sri Aurobindo and the Mother on the question of multiple Gurus. The gist of the matter seems to be that as long as you don’t feel strongly drawn to any particular sage, it is permissible to draw inspiration (through reading and interaction) from multiple sages. But once you get initiated by a particular Guru, you must stick to that Guru, otherwise the spiritual energies of different Gurus can interfere to create a frightful mess within your consciousness. Furthermore, if you have reached the apex with one particular Guru, you can certainly look for another. The cases of Kapali Sastry and M.P.Pandit can be cited in support of this clause; they were initially disciples of Ramana Maharshi but later choose Sri Aurobindo and the Mother as their Guru.
Note: These remarks apply only to Gurus who give personal initiation and individual guidance, as was typical in the past. These days, we see Gurus who offer Yoga courses through a network of trained teachers. My guess is that switching between courses offered by different Gurus should not cause any problems. It depends on the methods being practiced.
Dilipkumar Roy(1897-1980) was a talented musician who joined the Sri Aurobindo Ashram in 1928. Like most over-eager neophytes, Dilip wanted others to accept his Guru as their own. He sought to pressurize Sri Krishnaprem (Ronald Henry Nixon) who lived near Almora with his Guru, Yashoda Ma, to come to Pondicherry and meet Sri Aurobindo. The following anecdote is from Dilip’s book “Sri Aurobindo came to me“:
Personally, I came to profit most from the mystic wisdom of two persons I had come to know intimately through the love and admiration they inspired in me from the first: to wit, Sri Aurobindo and Sri Krishnaprem. When I say this I do not, of course, include the great saints and sages of the past who had won me over to their light long before I met these two great personalities. I only stress hereby the sense of blessedness that accrues to us when we have actually communed with the spiritual figures we have adored. This was borne home to me more and more as I grew to love them more and more, because, among other things, each in turn buttressed as it were my love for the other. But that is not the whole story; for I must add here that I felt not only refreshed but fortified by Krishnaprem’s bowing down to Sri Aurobindo. Happily, I was instrumental in bringing them into direct contact again and again through the letters they went on writing to me which, by and large, served as the bridge between them ever since I had built it accidentally to draw them closer to each other, even though there could be no question of Krishnaprem’s accepting Sri Aurobindo as his Guru. In fact, once, from Almora, he wrote to me, years ago, in reply to my invitation, that although he had the deepest reverence for Sri Aurobindo, he did not feel like coming to Pondicherry since he could get all the inspiration he needed from his own Guru. A little hurt by this, I went to the Mother with his letter. To my surprise, she not only supported him but actually praised him to the skies and told me: “That is the ideal attitude for any aspirant who has already accepted a Guru: to wit, to stick to him, refusing to turn to any other Master for Guidance.” Sri Aurobindo also wrote to me when Krishnaprem contended that all true Gurus were the same.
“All true Gurus are the same, the one Guru, all are the one Divine. That is a fundamental and universal Truth which justifies Krishnaprem’s statement. But there is also a truth of difference; the Divine dwells in different personalities with different minds, teachings and influences so that He may lead different disciples with their special need, character and destiny by different ways to the realisation: that justifies Krishnaprem’s own action. Because all Gurus are the same Divine, it does not follow that the disciple does well if he leaves the one meant for him to follow another. Fidelity to the Guru is demanded of every disciple, according to Indian tradition. Krishnaprem has that fidelity; he feels the spiritual tie holding him to his Guru in life and even after her departure; that is why he cannot think of going to someone else. ‘All are the same’ is a spiritual truth, but you cannot convert it indiscriminately into action; you cannot deal with all persons in the same way because they are the one Brahman: if one did, the result, pragmatically, would be an awful mess. You yourself have always in your heart laid stress on the principle of fidelity; Krishnaprem does the same so you ought to find it easy to understand his standpoint. It is a rigid mental logic that makes the difficulty, but in spiritual matters mental logic easily blunders; intuition, faith and a plastic spiritual reason are here the only guides.” 
These are two conversations on this topic. They are self-explanatory.
Purani: Dr. Kantilal has two questions to ask. First, can one have more than one Guru? Dattatreya had about twenty Gurus, he says, and profited by each. From a bird he learnt something, from a butcher something else and so on.
Sri Aurobindo: Such Gurus one can have even twenty thousand of. Why only twenty?
Purani: His second question is: Can’t one make spiritual progress by seeing the Divine in the Gurus?
Sri Aurobindo: The Divine is in everybody. So he can see the Divine in all. Why only in the Gurus?
Nirodbaran: But in the spiritual teachers one can feel the Divine more easily because they have realised Him.
Sri Aurobindo: That does not mean that the Divine is not in everybody. If one actually sees the Divine, it is a different matter. But if it is a question of thinking, one can think as well that the Divine is in all.
Purani: He asks if one can’t have more than one Guru and if it is disloyal to change one’s Guru.
Sri Aurobindo: If one wants to get somewhere, it is better to have one Guru and stick to him. Only under exceptional circumstances can the Guru be changed.
Purani: He says he has visited many Gurus but nobody has satisfied him.
Sri Aurobindo: That is not the fault of the Gurus. If he goes on changing like that, he will get nowhere. Moreover, there will be a play of contrary influences.
Champaklal: But if one visits spiritual people one can get some help on the spiritual path. They say that Satsang (company of holy people) has a great value in life.
Sri Aurobindo: Yes, one can get some influence, but that is for ordinary people who want some good influence to help them in their lives, not for those who want to do Yoga. Besides, even then there may be a conflict of influences -different people’s good influences may also conflict.
Purani: What one has gained from one may go counter to what one gets from another. Now I understand why you asked Dr. Kantilal to quiet his mind. His mind seems to be roaming about from place to place. (Sri Aurobindo was smiling at this. ) 
Another recorded conversation goes as follows:
Purani: There’s a lady who used to feel your presence in her own home, just as at Darshan; but last time on her way home from here saw Ramana Maharshi and then lost that feeling.
Sri Aurobindo: Naturally.
Purani: At first she couldn’t detect the reason why. Then she suspected the cause and I told her the Mother didn’t approve of mixing up things. Now she thinks it must have been due to that visit.
Sri Aurobindo: That was another influence. Besides, if Maharshi had been alone, it would have been different. But there are always other people around.
Nirodbaran: But the purpose is the same – seeking for spirituality—and it is in the same line.
Sri Aurobindo: That is not the question. (After some time) Purani received something from Lele.
Purani: Oh yes, I know to my cost. He gave me a terrible fever just when I was in the peak of health; the fever left me only after I received a letter from here. My encounter with another Yogi gave me vomiting, giddiness, etc. Otherwise I got nothing from them.
Sri Aurobindo (smiling): But Lele did give you something after all.
Purani: Yes-but I didn’t go to him again. Another friend after coming here asked me if he should go to see some Yogi. I told him he should not. He replied, “What’s the harm? It is the same spirituality.” I explained, “Maybe, but there are different spiritual energies and one may oppose another.”
Sri Aurobindo: Quite so.
Purani: But the man didn’t believe me. And he has paid the penalty for five years. He still hasn’t come here again! .
Exceptions have to be made for exceptional souls, such as Vasistha Ganapati Muni (aka Nayana) (1878-1936) who was a disciple of Ramana Maharshi. On the Mother’s invitation, he came and stayed in the Sri Aurobindo Ashram for a fortnight. These are some brief details of his stay as recorded by an Ashram inmate:
Aug 13, 1928: Recently S. Doraiswamy gave a copy of Uma Sahasram (a composition by Ganapati Muni) for Sri Aurobindo’s perusal who seemed to have deeply appreciated it. And the Mother expressed on her own: “If Ganapati Sastri is inclined to come for the August 15th Darshan he is welcome.” It was communicated to Nayana at Tiruvanamalai. Sri Ramana (Maharshi) seems to have said ‘When this suggestion by the Mother came unsought by Nayana, it must be a Daiva Sankalpam(Divine Will).’
Aug 15, 1928: Sri Aurobindo’s birthday celebration on the Ashram — and all of us had the privilege of Darshan of the Mother and Sri Aurobindo. Nayana, though pessimistic at first, after he had the actual Darshan, expressed “O, divya murtulu—O, Divine Personalities!” so much so, he stayed on till September 1st.
Aug 16, 1928: Nayana’s interview with the Mother for 30 minutes. They meditated together; Nayana felt spiritual current passing into him from all directions. Later on the Mother said to S. Doraiswamy: “He is the one man who immediately entered into my spiritual consciousness and stuck to it to the end.”
Aug 18, 1928: Nayana’s second interview with the Mother for 45 minutes. He recited verses composed on the Mother. Talked of present Avatara. The Mother got into trance. Nayana perceived light passing through her toe and then a glowing halo around her entire being, the whole atmosphere surcharged with divine current .
You can read more about Vasistha Ganapati Muni (Nayana) here
- Dilip Kumar Roy, Sri Aurobindo came to me, pp 320-321.
- Nirodbaran, Talks With Sri Aurobindo, Vol 1, p 432, 9 February 1940.
- Nirodbaran, Talks With Sri Aurobindo, Vol 1, p 272, 30 November 1939.
- K. Venkatraman. My Diary-leaves, p 363.
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