Guru or Spiritual Master: Adjustments by a Guru

                                                                  Q. We are taught to accept Guru as he represents the disciplic line. I've read and heard that guru always speaks without deviation from the previous Acharya in the line. I was wondering about the difference between Sri Madhvacharya and Sri Chaitanya Mahaprabhu. Specifically as it pertains to our line, and the question of authenticity.

                                                                  Q. If Buddha and Krishna are the same Person then why is there a contradiction in Their teachings? While Buddha preached non-violence, why does Krishna justify anger and violence?

                                                                  I have seen that over time, some of the teachings of Buddha have been modified to suit the times. Could the same have happened to Krishna's teachings also?