brake pressure

[mehoff400]

i recently swapped my 66 to cpp power brakes and calipers up front. i ran a few new lines to the front and rear. today was my first time really testing the truck out. all seemed good until after driving it for about an hour or so it seems i am loosing pedal pressure. I looked all around for leaks and what i do find is some fluid on top of the proportionate valve. i tighten it up the best i could but it didnt budge. should i use some type of teflon on this fitting? any other suggestions for things to look at.