OEM for master cylinders???, 69 BB Cuda - looking for replacement gasket

[cgfen]

The master cylinder in the Cuda works well, but the gasket allows fluid to leak and made my freshly re-painted MC look pretty bad in less than 2 years.
The gasket seems to fit well and the rubber is "soft / pliable", but I'm going to try and find a replacement gasket.

Some photo's of the numbers on the cylinder are below.
It looks like Dorman might make a range of gaskets.
Any other vendors you know of?

Numbers on the MC are
3699263 R2 on bottom spine
2427 or 2421 on mating flange.

 

[volunteer]

I would suggest to anyone getting a new or reman MC to check the contact surface of housing and dress it up with med. emery on hard flat surface. One in picture looks a bit rough.