Just received a newsletter from Lama Yeshe Wisdom Archive and they mention advice Rinpoche has given to students regarding other teacher's manifesting sickness. I thought it would be beneficial to reproduce it here:
Regarding the guru having sicknesses, and whether to have treatment or not, this answer is not for every single guru, but a general answer.
The disciple should pray for the long life and health of the guru, because disciples’ prayers have power. Why? Because there is a Dharma connection.
You can’t leave this out, saying, “This is Buddha, who does not need anything,” and then do nothing. Because the guru is showing an ordinary aspect, such as having suffering and sickness, you should offer service, get medicine, and so forth. The need for your service is also part of the manifestation, and it is for us sentient beings to collect merit and purify. Those sentient beings who offer service need their negative karma to be purified. These are the reasons for the guru’s sickness, because it makes possible very powerful purification for sentient beings, for them to achieve enlightenment quicker.
It is good to recognize this. When Lama Atisha showed the aspect of diarrhea and loss of control of his bowels, Drontompa cleaned it with his hands, without any thought of its being dirty, and from this he achieved clairvoyance. Because his mind was clarified from these actions, he was able to read the minds of sentient beings, even ants, even the minds of people as far away as an eagle can fly in 18 days.
Thank you very much for your concern and for your guru devotion. That is your jewel, the root that eliminates all defilements and obstacles, and achieves all realizations and enlightenment, and enlightenment for all sentient beings. (Advice given by Lama Zopa Rinpche).