I'd start back at the beginning and get (2) brass inverted flare plugs from the Edelman" fittings cabinet at your parts house. They're cheap and the end will have an inverted flared "cone" a mirror image of the brass seat(s) in the M/C ports. Cap the M/C & if it good (& bled out) the pedal will b rock hard w virtually no travel. this'll elim the M/C & you can concentrate on the prob valve (blockage of some sort) or one of the 4 corners. "air"