leaking brake valve

Waco,
A photo would sure help, pointing to the spot it is leaking. I envision the same adjustable proportioning valve I used in 2 cars. Those require 1/8 NPT to 3/16 inv flare adapter in each port. If leaking at the NPT thread, you need a better sealant (teflon tape or such). If leaking at the inverted flare, it is probably a bad flare on your tubing side, or you got it in cocked (as mentioned). Neither are the fault of the prop valve manufacturer.