leaking master cylinder cap.

That’s odd. I’m using the Mopar performance light weight cylinder with no issues, other than the cap will leak if I have it jacked up too high in the front or rear.
Yep that’s understandable, I have mine half full trying to make it quit dripping out the cap. Still leaks! I think what happens is when you hit the brakes hard it sprays straight up and leaks out of the seal. I’m about ready to just make a drip pan for it. Not sure what else to do