Just so happens that I am doing the spring replacement on the SDL today.

Some things to note:

1) The original spring caused the driver to sit lopsided in the seat. The left side of the seat feels lower than the right side. Classic sign of broken springs. After taking the seat apart, the spring was broken in three places! The cost of the replacement spring is about $200. Your alternative is to go to a junkyard and buy a passenger side seat spring. The chances that this spring is not broken are quite good. However, the new spring is of a better design and has a stiffer connection at the front.

2) I did not purchase the replacement horsehair pad. This was probably a mistake. 20 years of sitting on the pad has caused it to deform a bit. It will probably still do the job, but a new one would be better. I did get some memory foam to stuff in between the old horsehair pad and the leather cover. It causes the cover to sit up a bit in the center. I did not have the memory foam go out over the side bolsters because of the potential problem of installation.

3) The most difficult part of the job is to separate the lower frame with the motors from the bottom seat cushion. Several electrical connectors must be disconnected and the motor bracket must be loosened. Took some thinking to get it off without any damage. Hopefully it goes back together OK.

4) It's definitely worth it to remove the electrical connections because several wires have worn right through at the points where the wire ties held them to the seat bottoms. 20 years of vibration with the plastic ties is too much for the insulation! I have a problem with the SD where the seat will move spontaneously! I'll bet that this is the cause.