Master Cylinder leaks

Help I have a 68 cj5 that the PO switched the master cylinder to a newer firewall mounted unit when he upgraded to 11" drums (era 1974).
It was leaking fluid and the booster was shoot ,so I replaced it with a complete unit from napa ,now it seems that every time you use the brakes fluid drips out from under the dual reservoir cap,like it's over full????
The seal on the cap looks good ,the cap itself sits in place well ,the reservoir is only about half full ,I don't know what else to try ,I wouldn't think that the heat from the motor/headers if affecting the fluid that much.:?

Any idea's?

Thanks
George

 

Check and make sure the cap is not warped, and the rubber gasket is not bad.

 

Did you try putting the seal on the master bowl first and then the cap?

 

The seal is attached to the cap with little tabs,but it looks good

 

I got the same problem, I think it the gasket that too small.

 

I have the same exact problem with my Napa mc.
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I just recently did this for my neighbor. Removed gasket from cap and wiped dry with rag. Wipe the top of reservoir dry. Press gasket firmly around top of reservoir and snap cap on. Then grab the rubber tabs and pull and half twist and they will go into the lock position. No more leaks.