1977 Chevrolet Truck master cylinder

are you sure it' snot residual brake fluid in booster? there is non vacuum on that side of booster. if there is the booster needs a new diaphragm. Is the fluid level actually going down in master?if it is the same type of master try another supplier as so much crap comes from china so that may be the problem.

Yes, the master cylinder is definitely losing fluid. As I said, this being the third one with the problem at not changing I wondered if it's possible that could be something with the vacuum booster. I never ran into this before nor has anyone I have spoken with. Would having be wrong booster on the vehicle by any chance cause that? As I said this being the third one and the first two being rebuilt and is the last one is supposedly from the factory. And the problem still exists. Once again if anybody can help me with this problem I would greatly appreciate it. I thank you for your help.

On that pickup there is 200,000

the only way the booster could do anything is suck fluid from the master which I doubt I have never seen that. like I said try another supplier as the on you are getting may just be poor quality.

I want to thank you guys for once again for trying to help me. I will tell my buddy that he has to buy from a reputable dealer. I believe he's willing to try anything once. Once again thank you very much for the help.

wel it's ironic as I've done this for 50 yrs and have never seen a New master do that bu the junk that comes from china hard telling. Rebuilt unit I have seen but not new.....