After only about 300 miles of driving, my rebuilt '69 master cylinder ( a correct one ) is already leaking at the back down my booster:(.

I was wondering if I should have it done again, or get a reproduction unit from Ground Up with the proper bleeder screws?

I was talking to my mechanic ( 30+ years experience ) and he stopped using rebuilt units in the mid 80's. He said the last straw was when he had a rebuilt unit leak while bench bleeding it.

I'm not concerned about date codes, just a correct appearance.

Any opinions?

When I was a kid, and with my old Charger project in the 80's, I tried rebuilding wheel cylinders and a master cylinder. None lasted very long. So I quit doing it, and just buy remans from Carquest, Autozone, Napa, Advance, etc.

That has worked well since then.

It may be best to get a reman unit to install, pay the core, and keep your orig. It can be sent to one of the speciaty places for an in shop rebuild if wanted.