Membrane in the shifter of something else?

Three weeks ago I fall down. I rode my bike without any issue after that. Last Sunday I did 3h in the freezing fog. On the Monday I wanted to ride the bike again and when I press the break the oil spilled out. When I refilled the system I could see that it came out of one tiny hole. Is it the membrane problem or the shifter is trashed?
I'm also not sure about the visible crack in the front of the shifter. The other one doesn't have it. However the crack looks so darn straight that it seems to be there from the day zero.