I had my master reconditioned a while ago, but wasn't ready to stick it on the car. So of course while it sat wrapped in the box of bits waiting it's now covered in surface rust.
I'm guessing I need to get it off, especially from inside the pipe holes, before putting it on.
What would be the best way to do that? And is it possible to do it without getting crap in the actual cylinder again?Or should I just take it back to the brake shop and get it pulled down and sorted properly, seeing as brakes are kinda an important part of the car?

If that thing has been resleaved in stainless steel then you might be in luck.Why not fill it up with fluid and let it soak for a while then gently move the piston taking note of the fluid quality thats coming out and resistance? Or if its already been pumped why not just remove and inspect? Not a lot to lose at this point.