IIRC there is nothing there but the rubber boot that "clips" onto the outside of the master, and the seal on the piston. Probably need to be careful re-installing the piston past the snap ring groove, and you are right, if it's old, it may be a better idea to just replace it.
I didn't notice mine was leaking for months. It was an extremely slow "leak" and I never felt it in the pedal.