Why is my brake reservoir leaking

[dlisabeth]

I have a 1965 C10 with the following brake setup: 85' C10 front discs, stock rear drums, '97 S10 brake booster, '85 C10 proportioning valve, and '85 C10 master cylinder.

I am having an ongoing issue with the '85 C10 plastic brake reservoir leaking and ruining the paint on my inner fender and frame rail. I purchased a new brake reservoir, cap, and seal in hopes that it would correct the problem, unfortunately it did not. I have now cleaned up the mess and repaired the paint 3 times and am out of ideas. What could be causing the reservoir to leak? The brakes work great and there is no indication of a problem until I open the hood and see the damage that has occurred again. The only thing that I have noticed is small geysers (no air bubbles) in the reservoirs when the brake pedal is pressed with the cap off. I have done some research on this and it seems very common. Does anyone have any thoughts? I would love to solve this issue so that I can drive and enjoy my truck without constantly wondering how much brake fluid is leaking.

Thanks for the help