The first thing to do is to take the car to the body shop, and make sure the
seat is not "leaning" left or right. Even 1/2 inch difference makes *all* the
difference. My STS was a pain to drive, and I don't have back troubles. The
left side of the seat mount was 1/2 inch lower in the back corner that the
rest of the mounts. $18.00 fixed it-and I still have the car.(1994 model)
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.