I converted my 68 Dart over to front disc brakes from a 1973 Duster system. The problem is when I pump the brakes fluid dumps out from under the cover. Leaks right under the rubber gasket. Fluid level about about 1/4" from top of reservoir. This is the second new master cylinder I put on and both did the same thing. Do I have a bad proportion valve? Never had this happen before, did this conversion many times. Brakes work fine. Lines all put on correctly, checked twice. Checking to see if this happened to anyone else.