My brothers 2000 F-350 (with a 7.3) has had some trouble. Some power steering fluid accidently got put into the brake fluid resiviour. After the incident, the brakes became real soft, as in the pedal had to on the floor to get stopped. After I heard about it and drained all of the fluid out of the lines, resiviour, and calipers and filled with new brake fluid. I bled the brakes until new fluid was coming out of all four calipers. After a few days of driving, but still soft pedal every once in a while, things are back to the same old thing, pedal to the floor. When the brake pedal is pumped you can hear a lot of what sounds like air coming from around the resiviour somewhere. Does anyone have a clue of what I can look for.