I bet it's the master cylinder o-ring, look at the area between the master cylinder and the power booster. If it's leaking you can tell because the paint is soft or missing below them, on the fender well or the booster or both.
If it's the master cylinder replace it with a rebuilt one, only $30 or so and do a search, on here, on how to do it.

Michael j

TreadLightly! Trainer

Grasscat III, 1994 Gen 2 Five speed, Stock ( for a little while )

GrassCat II, 1998 Gen 2.5 Locked and loaded. Ran off with Hector.

GrassCat I, 1991 Gen 1 Ran off with Justice.