Slow Z2050

[DogT]

I've had this Z2050 since 2004. I've got less than 550 hours on it and already one of the motors/pumps is slow. I have a verrry hilly location and prolly wore one side out mowing on the hillsides. How can I tell if it's the pump or motor? Is it a huge project to change either or both? They are both rather expensive. The B&S engine is in good shape and it cuts good although I've reinforced the deck with some 1/4" aluminum plate on the front edge. Just the other day I replaced one of the pump to motor lines, it was leaking pretty bad but that's not the problem.