There is a rubber seal that goes around the pushrod between the master and vacuum booster. If that is missing, the vacuum booster can sometimes pull fluid past the secondary seal of the master. It's about as big around as a fifty cent piece and about a quarter inch thick. It also keeps fluid from a leaky master from entering the booster.

 

The seal is not a problem and the small push rod coming off the booster is non adjustable, I more or less was asking about if the under dash rod adjustment would help me with this problem. or if it may be a another problem I'm overlooking. The rear brake fluid res seems to be the only one leaking down.

 

Just a thought,
Is your pushrod hooked to the correct hole on the pedal?
There are two points to connect to. One for power and one for manual brakes.
Also, the power brakes do not use a return spring.
Lastly, who is the rebuilder? Maybe they are not doing a good job?

 

Brew I'll have to look at the rod to see which hole it's in as well to see if the return spring may be installed, which hole should the rod be in 1st near firewall or 2nd?

 

The lower hole is for power brakes, at least from memory. The wrong one puts the rod at an awkward angle.

I would find a new source for master cylinders. And get new ones, not rebuilt.