The diksha guru is like a father, and you can never reject a father even if he commits some transgression. One’s being a father is not dependent on his making or not making transgressions but on a simple biological act. Similarly, the Guru is guru, not because of any material deeds good or bad, but because he has established for the disciple a real connection to a particular spiritual ideal and practice. In other words, the guru literally gives life to the disciple. So to reject the guru means to reject the life that he has given. And many people do so rather hastily which results in their own spiritual detriment.
There is no way to find the guru inside our heart without first recognizing and appreciating the grace of the Guru standing in front of us. As a disciple, I expect the guru to be perfect because I have a psychological need for such perfection. And if the guru disappoints me, I become angry as described in the Bhagavad gita (2.62-63). Then I forget whatever grace he did gave me (smṛti-bhraṁśa) and I lose my intelligence (buddhi-nāśa).
The main error here is that we have not really seen the guru’s grace for what it is. Instead we mistook something else to be his grace: his wisdom, his charisma, his power to give boons, the ego-expansion that comes from having a famous guru, etc. If we recognize the grace, then we will pursue the perfection that it points to.
Everyone will agree that bhakti is the path of Grace and Gratitude. The Guru embodies Grace and is therefore the principal object of gratitude for a disciple. The Grace that came through the Guru WAS and IS real; it is part of the eternal stream of grace that continues in all time and place. If we find fault with the guru, the flow of grace stops.
Guru’s grace is tangible, and it manifests to the disciple in the form of many wonderful divine assets. In Mukta-carita, Srila Raghunatha dasa Goswamipada mentions all the transcendental gifts that he as a disciple received from his Guru: