new master cylinder or rebuild?

needsaresto said
The raybestos # I have for a new replacement master is MC 36221.

Again, that is a drum/drum master cylinder. You said you have disc brakes, din'tchya?

only available in cast iron.

Correct. There aren't any 4-bolt masters in aluminum. They're all cast iron.

Hey Dan; Is MC 336421 cast as well?

Donno; the one I pointed you at is MC36412. Yes, it's cast iron.