Much is written in Chasidic books about the importance of looking at the face of a Tzadik (and to the converse, the Gemora says it is forbidden to look at the face of the wicked)Here are several stories in that vein.
About the great Tzakik Rebbe Reb Mailech (Elimelech) of Lezhinsk (many spellings of this city name), it was known that one who had merely seen his face, could not die without repenting. Many years after his departure from this world, an old lady came to Rebbe Hershel Rimonover, his disciple's disciple,with a strange request. She told the Rebbe's gabbai (attendant)that she wants the Rebbe to pray that her father should die already. The gabbai fumed at her-how do you dare ask him to do such a thing? She explained that her father is over a hundred, bedridden, in a loft, and she, in her old frail state is the only one who can take care of him, and she has no more power for it. And he himself wants to die but can't. The Rebbe heard the comotion and left his room to see what was going on. He sensed that there was something special behind the story. He asked to be taken to visit her father. The Rebbe asked him about his life, if he had kept Shabbos, put on tefilin, eaten cosher,etc. He replied negatively. What was your livelihood? he asked. I was a wagon driver. Did you ever see a Tzadik in your lifetime? Yes, he said, once I took that red Rebbe Mailich on my wagon. On the way, he stopped for a while to pray and I am sure he was drinking a lot of whiskey, because his face was red as a beet. The truth was, his face did become red before praying, but not because of alcohol, rather from his fear and excitement to speak before the Allmighty. Rebbe Hershel started to explain to him the basics of Jewish belief, the giving of the Torah, the mitzves that every Jew is obiged to perform. The old man started crying. Rebbe Hershel asked him, if you had known, would you have performed the mitzvos? Of course, Rebbe, he replied. As being a cohen, who is forbidden to be in the house with a dead body, the Rebbe quickly ran outside, knowing that the man's time had come, because he had now done repentance, and could move on to the next world.
Seeing once a Tzadik saved his life! An architect from Haifa, working in the U.S., was "caught" going on a plane to visit the grave of the holy Belzer Rebbe, Rebbe Aharon Rokach. What was his connection? He told the Belzer chusid on the same flight that as a child, he saw the Belzer Rebbe only once, when the latter came first to Haifa after escaping Nazi Europe. Recently, he dreamed that he was standing next to the building he was presently working on, when a porch suddenly became detached from the wall and fell on him. He found himself amongst the rubble, and he saw the Belzer Rebbe tell him , you can get up and go. The next day, that is exactly what happened to him, and miraculouly he was not even injured. Later, he dreamed the Rebbe again, and told him his name, place of burial and date of yortzeit.