Power Steering Failure

Having power steering problems with my 1996 Seville. It started leaking fluid but the source was not obvious to my mechanic. On the hoist with the steering wheel rotated side to side you would think the leak would be obvious ....so not likely a pressure side of the system?? On the second visit we elected to replace the pump ....which worked fine for about two weeks and now I'm once again losing fluid. Any one had a history of this ? Could I have replaced my pump with one that was about to fail ??