new proportioning valve leaking

Latest update: turns out I was mistaken about the manufacturer. I called Dr. Diff who told me the manufacturer is actually a company called MBM. They also occasionally have the problem of the crush washer not sealing, and it can usually be fixed by simply tightening the hex. To get enough leverage, you have to use a crescent wrench to hold the valve body while turning the hex (to get space for the crescent wrench it helps to unscrew the valve from the vehicle frame, and also to loosen the front brake input line from the top of the hex). Doing that I was able to get about 1/8 turn and it looks like the leak has stopped for now. I'll update again if that didn't fix it.