FWIW, I have been working on my own cars, worked my way through HS & College and for a few years after college in the father inlaws garage for over 30 years. I have never replaced a master cylinder with anything but a rebuilt and have only had one failure, if you can call it a failure.
The one failure was recently when I did the swap to disk brakes. The casting for the MC had a void along the surface where the cap seals that did not clean up during the machining resulting in fluid leaking past the cap. As with any rebuilts I buy it came with a lifetime warranty and I just brought it back for another.
