American Motors: 79 CJ 7 master cylinder leaking..., fuel line hose, rubber gasket

Question
I just bought a 79 cj7. My husband took the master cylinder cap off to check the fluid. Now, we have problems with the cap leaking.  We have tried the following: check seal, bar, and cap. All seem fine. Put a washer, fuel line hose, and heater hose between the cap and bar on top.  Finally, bought a reman cylinder and took the cap and gasket off. Put it on the old master cyl. Still leaks.  tried tweaking the bar even. still leaks out of the cap. Had several people look at it and everyone is clueless.  doesn't have too much fluid, only leaks when drive down road a ways. any suggestions?

Answer
Is the push rod aadjusted properly? If it too far out, it could prevent the master cylinder from releasing.
Also, is there any possible way the brake fluid is contaminated with something? Oil in the fluid would make the rubber gasket soften & swell.