One problem related to power steering fluid has been reported for the 1999 Buick Regal. The most recently reported issues are listed below.
August 2017', the steering began to pull very slightly left and right at all speeds but more noticeable at low speeds or when turning the wheels at a stop with a very slight clunk noise that got louder over the year. Visible inspection at my repair shop during a flat rear tire repair did not find anything worn out or damaged but suggested maybe a ball joint could be getting old enough to need replaced as it did have about 158,000 or so miles on it but they couldn't indicate if it was a ball joint specifically as there was no unusual movement or noise from one. I also checked and found no issues with any component underneath. No leaks and power steering fluid was good. Then September 7, 2018', while driving around town the steering made a loud clunk steering left and really began to pull especially left. I got it home 3 miles later and put it on ramps and had someone work the steering wheel back and forth and I found the clunk is coming from the drivers side of the rack and pinion assembly. You can literally see it jump when it clunks. After this stationary test the steering was much worse, the car was not drivable f the block with out heavy effort on the steering wheel so it is parked until it can get fixed. Complaint history for this issue with gm vehicles in this +/- 2 year range is alarming.