If you can remove a master cylinder, you can rebuild it.
There's a spring clip that holds all the insides in, and other than that, all you'll need is a cylinder hone.. You can pick one up for $10 at the auto parts store.
Lubricate it with brake fluid and runt he hone at medium speed on your drill.
Getting the rubber seals back over the brake piston is the only tricky part.
But that's $10 for a tool, and $10 for the seal kit.
It's worth a try!!
All that being said, a reman is just as good as a new unit.