It can be very difficult to get the HP line out; those suckers are Tight, and the only way I did it was with the pump on the bench, flare nut wrench on the fitting, big vise-grips holding the jaws of the flarenut from opening, then a Lot of force. I don't know how I'd have gotten it in the car. Oh, I replaced the pump and the line.

I think maybe change/flush the fluid, use a turkey baster, and see how that is. Then there are the strut bearings, which I think is the most likely really.