There is a story about the Tzemach Tzaddik that some of his chassidim were preparing to visit him and they were discussing whether they should do teshuva before seeing him or let the Rebbe see them as they are and let him help them do teshuva. When they got to the Tzemach Tzaddik, they were astonished when he told them (without them mentioning their discussion) that they have to do teshuva, but their Rebbe has to be able to see what they were like even before.
Reb Elimelech of Lizensk said that when a yid puts his hand on the doorknob at his home as he leaves to visit his Rebbe, if the Rebbe doesn’t know he is coming – then he isn’t a Rebbe.