power steering problem....i think

i have a 97 gp gt with 80k miles and recently the steering has been giving me a bit of trouble, most noticeably when i'm either pulling out of or pulling into a parking space at low speeds...

when i let the car idle and try to turn the wheel it is smooth until i get to around 90 degrees in either direction and then it requires me to pretty much use all my strength to move it any farther... now this problem is not noticeable at all when i'm driving at speeds greater than 10 mph, and there is no real noticeable whining of a tell tale failing pump... checked my power steering fluid resevoir (they picked a great &^&%-ing place to put it by the way) and it was empty, so i added some and it was working fine for a day or two, but then same problem again, checked the resevoir again and its empty, so i fill it up again and lay some cardboard underneath the engine to see if i have a leak in the lines and so far nothing.... any ideas would be fantastic...

Power steering pump is a possibility but so is the rack and pinion based on your symptoms. The PS fluid has to be going someplace. Most likely a leak. Another issue I've seen is the inner seal for the rack and pinion will blow causing leaking. The fluid collects in the rubber accordian boot that covers the inner tie rods. Also, check the pressure and return lines from the pump to the rack and pinion to include the area around the pump pulley.