I have a 1991 DeVille that is in great condition. Bought the car several years ago and at that time done a complete brake job on the car. Recently I have had a problem with the brakes. The brake pedal will travel to the floor and they feel soft/spongy. You can pump them up to stop the car but the next time you apply them they are right back to soft and traveling to the floor. I changed the mastercylinder and bleed them but with no inprovement. I bleed the brakes after driving for a while and got more air from the line but still no luck. Can someone please tell me what else I can look for or do to repair this problem? Tahnk You!