Brake master weeping

Funny you should mention a defective MC. I have heard of people installing the cups in backwards, which would force the fluid up and not down the lines, but I'm sure you would notice the brakes not functioning.
My brakes always worked excellent. minimal pedal travel, car stopped as it should have, the only issue was the constant leakage. The calipers were fresh, as were the rear cylinders, all of pads, shoes, the lines and hoses were new, even the master itself was a rebuilt one, installed when I did the disc conversion. It had sat on the shelf for a couple of years, but was still dry and in the box so I did not believe that should have been an issue.