I have a MK4 complete kit with manual Mustang GT disc brakes. It has the Wilwood pedal assembly with separate brake reservoirs for the front and rear brakes. I have bled the system several times without much luck to get a hard pedal. I first used a vacuum pump to suck out the air. Then I got my wife to push down and hold the pedal while I opened the bleed screw and drained some fluid into a jar of brake fluid. I got a small amount of air out the First time and then all fluid. We did this several times. We had a hard pedal for a little while. When I went for a test drive I would periodically have a hard pedal then The next time the pedal would go to the floor. This was my 3rd go around at trying to bleed the brakes. When I installed the Wilwood pedal assembly with dual master cylinders, I did not bench bleed the cylinders. I was unaware that I needed to do that step. Today I went to 2 different auto repair shops to see if they could pressure bleed the system. Since the brakes were soft intermittently, they thought that the problem could be one of the master cylinders are bad. They said if I still had air in the lines the brake pedal would be soft all the time. I'm at a loss as to what to do next. I would hate to buy a master cylinder if that's not the problem. How to do you test for a bad master cylinder and how do you determine if it's the front or back one?