Just found this info elsewhere for a '98 LaSabre...so might help you with your '99:
As you are looking at the engine from the front, it is at the back left, a little under and inside the rear serpentine belt pullies. It's hard to see, but if you look from the inside, down the back of the motor by the firewall toward the belt pullies, you should be able to find it. It is more difficult to access if it with a turbo. No wonder GM is going down the drain.
I would suggest getting a siphon tip for the Power Steering fluid with an on/off valve...I just added fluid to my 96 and could not have done it with out this tip because of the amount of time it took to maneuver the fluid container to the reservoir opening while holding the container upside down.
what type pf power steering fluid take for a 94 buick lesabre
pictures of where to put power steering fluid in a 1990 buick lesabre
Owner's manual.
If you have plenty of fluid it could be the power steering pump itself going bad or it could be the rack and pinion assembly.
it can overheat and burn up
The power steering fluid dip stick is made to the reservoir cap. Pull the cap off to read the stick.
NO the transmission fluid will cause the seals in the pump to leak
A 1995 Buick LeSabre takes 7.4 quarts of transmission fluid. Dextron lll transmission fluid is recommended for use in the Buick LeSabre.
Check fluid level, are there any noises, what are the conditions when problem occurs?
A 2005 Buick LeSabre automatic transmission requires 7.4 quarts of Dexron III fluid.
It is near the passenger compartment on the passenger side of the car. I have a 2001 and looked this up in the manual.
The first thing to check is the power steering fluid level. If the reservoir is low add some. Other then that, it can be the power steering pump is going bad, and will need to be replaced soon.