I have the squeaky driver seat problem as well with my 2002 TLS.
The weird thing is that it only happens when I make left hand turns. Surprisingly, it took me awhile to find out where the noise was coming from.
Looks like the lumbar support lever on the right side of the driver's seat is rubbing between the seat and the center console causing the annoying squeak. I have the lever all the way down. If I put the lever in the upright position, no more noise.

I haven't figured out what to do with it just yet. It is also the least of my worries. I have to call my dealer tomorrow about excessive road noise after my last service call. 18K miles on my car and no idea what can be causing it. It starts at around 30 MPH and gets worse from there on up. The noise sounds like it is coming from the front end of the car. Other than that the car rides fine. After reading the multipage post about transmission problems, I have a bad feeling...
TD