I was going to mention the same exact King pistons from the 1960s and earlier, yet on instruments found to have been taken care of and with original (rather than rebuilt) tolerances - or very close to zero wear.
My 32-inch tall 19-inch bell Holton B flat instrument (which has been seen and discussed here, and which many believe the outer bows and bell were probably York manufactured, due to some pretty convincing evidence) features a 1990s highly adulterated 2341 (I believe it was during the UMI era) valve set.
It's a very complicated setup, which - by the time the instrument was completed would have been a nightmare to pull that valve section off and have it upgraded from A- to A+ via a rebuild (and I just don't know if I would want to send a valve section off these days, because I don't have any experience with anyone other than THE Guru who retired from Elkhart).
A customer offered to barter some fairly extensive dent removal from his 24J Conn tuba in exchange for a set of those Meinlschmidt custom ported aftermarket King valves. My previous experience with those was that - unlike the substitutes for the the larger B&S valves, those made for King are often just a little bit oversized (which - for me - was perfect). Therefore, I didn't have to pay for the valves with money, and - by the time I fitted those aftermarket pistons into my King valve section - I ended up with like new piston to casing tolerances. Sometimes I live the life of Riley.
A bonus has been that - over time - I've been able to sell those four OEM King pistons to schools whereby their young scholars trashed their sousaphones' pistons.