leaking master cylinder cap.

Dragonsteel said
I have the same problem and did replace mine with the aluminum one with plastic caps from Dr.Diff and it still leaked although not as bad as the iron unit.

View attachment 1715712747

The caps and gaskets can be replaced. I've found that they will develop small leaks over time, or after you remove/tighten them a bunch. The other thing is that the bump on the cap corresponds to a small vent, so, point those toward the rear and not the front. The caps (#42044) and gaskets (#42081) are readily available, and fresh ones should stop any small leaks you may have.

Dorman 42044 Dorman Master Cylinder Caps | Summit Racing
Dorman 42081 Dorman Master Cylinder Reservoir Cover Gaskets | Summit Racing