Depending upon its' age, I would be hesitant to buy an NOS (New Old-Stock) brake part unless I could examine it first.For a potentially 50 year old part,my concern would be the rusting of the cylinder walls that could quickly cause scoring, thus leaking.Also,there is the likelihood that fifty year old rubber parts will have hardened,also with the potential to accelerate leaking in the cylinders.

This is true for either master-cylinders, or individual wheel cylinders.Go to a quality auto parts store,such as Napa.They can easily supply your parts,will stand behind them if there are problems, and returns of bad parts will be painless,as opposed to buying through the mail to save a very small amount of money.Finally, if you can, order name-brand as opposed to off-brand or no-name, the support will be better.Raybestos, EIS,are a few trusted names for brake parts,though nearly everything is coming in from that Oriental country across the waters, now.

Good luck.