Cadillac STS Forum - 2005 through 2012 Discussion, Bushing in the rear end in Past Cadillac Vehicle Discussion; Hi, check this thread out if you haven't already:
If you feel like doing it yourself look up Creative steel the sell a urethane bushing that is way better than stock. The y will also rent you the tool to do it very easy. Took me about an hour 30 to do it. The tool they give you presses the old one out and then presses the new one in. They give you directions with large color photos that are very easy to follow can be done in your driveway on stands.
Here is the bushing and the tool