The rear airbag suspension needs to be replaced.

If you are refering to your rear shocks you may just need the compressor pump, located under the hood on the left side. That pump may just be bad, especially if the car sit extremely low.

I Would go with springs. I understand people enjoying the air ride but I promise it is more trouble than it is worth. Compressors have a 100% failure rate. What will happen is the airbag will end up getting a hole or tiny crack in it so the compressor has to work extra hard because it is like blowing up a balloon with a hole in it. Therefor the airbag kills the compressor and you have to parts you have to constantly keep buying. With air suspension there is never a permanent fix. I would recommend going to strutmasters.com and taking a look at the conversion kits. these convert you from the airbag to a powder coated American made steel coil spring that is [U][B]guaranteed[/B][/U] to last the life of the car. And for a very affordable cost. I added the link below so you can check it out.

http://www.strutmasters.com/buick-suspension-parts-s/27.htm

I hope I was of some help

Good Luck!!!