General trivia: During the 80's there was a whole bunch of master cylinders pumped out into the market [and some OEM] with inferior castings, way too much porosity. They seemed to squeak by for several years, then interior wear takes effect. When a guy then rebuilds one & hones it out after some years of corrosion going on it then allows the junk casting to leak like a sieve. Same is true of slaves. Then in the 90's they got their act together again and a better product for a while. By now many rebuilt masters off the shelf from auto parts stores may also be from that junk batch in the 80's. Word is, buy new or get the best > stainless lined.