I got a 96 in my shop w/brake problems. owner said pedal would slowly go to the floor w/motor running and pushing on pedal. so I decided the master cyl. was leaking by internally. I put a brand new(not a rebuilt) master cyl on,flushed the whole system,and it did'nt help a bit. pedal still goes to floor w/motor running. but w/out the motor running the pedal is hard and stays right there like it should. can anyone tell me what the problem is?