This may be a long shot, but when I replaced the pump in our ‘90 740 Regina I didn’t get the pump properly locked together with the long flat bracket that is supposed to hold it in place. As I recall the bracket has a square hole near the bottom end that locks onto a matching square section that protrudes from the side of the pump. Consequently the pump ended up “blowing itself” downward, creating a gap between the top of the pump and the bottom of the pulse buffer unit (for lack of a better name). You need a good tight connection there. I had to go back in and correct my mistake.