i've always used new with master cyls. seems the euro-spec metal reacts differently than the us made stuff. sold rebuilt masters for years for us cars in the 70s and 80s. the only builder that had a decent rebuild for the euro stuff went out of business years ago. a lifetime warranty, also. if yours was sleeved, i'm impressed. hadn't seen that in a long time. if yours was sleeved, it's hard to believe there's a problem, unless the sleeve is too big for the piston or the seals were too small for the new sleeve or were junk to begin with. or, the outer seal of the piston is rolling in the bore and sucking air as the pedal comes back up. again, junk.

wanna avoid changing the master? change the fluid every 2 years. at the dealer in the 80's, we stocked about 15 masters for the 240s. about 85, volvo changed their rust warranty and said change the fluid. we changed the fluid and the later cars never seemed to need masters. done it with my cars over the years and customer's cars, also. been a long time since i've put a master on any thing i've serviced over the years, volvo, bmw or benz. good luck, chuck.