Weight loss.

When I got the master cylinder in 2009, they said disc/drum, however this was just after I returned a rebuilt one that the piston looked like some beaver gnawed on it! It does have equal size reservoirs on it, but the size difference was never an issue, I really should have gone looking more. I knew everything else was from the original K&H disc set up. Proportioning valve, distribution block, actually never cracked a bleeder and notice the drag go away or I would have scorched earth everything until I found it. Spent 1/2 an hour shooting brake clean through the master without the piston in it. Brake clean shot through every hole each way. Search online and found a video about how to remove them from a master cylinder. Very easy process. I’m slow because I’m FAT and stupid!