Unless your brake cylinder castings (master and wheel) are in excellent condition, I'd strongly suggest having then sleeved with stainless steel. It's a one time expense that will assure they can be rebuilt repeatedly. and a good polished surface on the sleeve will make those new cups last much longer between rebuilds. It's a pretty simple procedure that any machinist worthy of the name should be able to do.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!