A few months back I was having brake issues and I had no pressure when i applied my brakes . So i changed the master cylinder .When i went to bleed the system I wasnt getting any fluid to the rear brakes so I figured the system had something in it. SO I traced the problem all the way back to the proportioning valve and it was all gunked up.so I opened it up and a oring seal was broken inside. Of course I cant find anyone who sells them. I went to 5 hydralic places and napa and advanced and no body carries oring that can withstand the brake fluid. O and also ford discontinued the propotioning valve a few years back. My question is is an aftermarket propotioning valavem y last resort. and if so which one do i get I dont know to much about them? Thanks guys