Master cylinder rebuild or replace?

The store-bought MC I put in my 65 Newport started the "sinking pedal" within a few years. I pulled the piston out and found everything pristine inside, but the piston seal had been cut by a sharp edge. Apparently, the rebuilders honed the cylinder but didn't "break" the edges on the feed holes. Thus, one can do better at home. Not the first time I have found problems w/ rebuilt parts.