Brakes

I have a 71 MGBGT and had to replace the master cylinder, I need the O-ring that goes between the master cylinder and the resevoir can any one tell me where I can get one

A good hardware store usually has a large selection of generic o-rings.

Most generic o-rings that I have seen in hardware stores are in the plumbing section and are intended for faucets, etc.

My only question is whether brake fluid would attack the rubber in them. Since they are sold for use in water, they may be made of a type of synthetic rubber that can't stand up to petro-chemicals.

Could be. Maybe the thing to do would be to let it soak for a coulpe of days in brake fluid to find out.

Most auto parts stores have a selection of neoperne O-rings that they'll sell singles out of. Just get one that fits and stick on, it'll squash to fit.