Leaky adjustable proportioning valve

I don't know what thread was on the 3/16" inv flare fittings I put in my similar-looking prop valves, since they came with the prop valve. They looked like 1/8" NPT and I recall using a U.S. wrench. I do have 1/4" inv flare fittings that came in the box that I didn't use, so might check those (if I run across them). If you find it was a design problem, I would complain to Right Stuff, since you paid big $$$ for a BBP brake setup.