I did this job a couple of weeks ago and what a difference it made!
If the back is ok and only the base is collapsed, The base is the same drivers and passengers and according to mecedes parts dept. it has the same part no as the 126.
which means any passengers seat out of a breakers 123 or 126 will tend not to be as worn. Mine came out of a 1981 230
It took me 1/2 hr to take the passenger seat out and about 3 hours to do the rest of the job ( what pillock put a height adjuster on the drivers side)
a mate found this on another site and sent it to me and I found it covers most things
Replacing Seat Springs
If the plastic handles are broken (manual seats), they can be replaced. The replacements have bolts.
The seats come off with 8mm bolts or philips screws (same with the seatbelt rail).
Unclip the seatbelt warning cable, if applicable. [On non-adjusting seats a sideways bolt is also there on the outside tower. The manual seats have a rectangular washer to block aft movement. Speculate as to its purpose and toss it.]
Lower seat rails must come off first. [This is to expose the middle screw attaching the upper seat rails to the seats.]
Set seat to forward position (tracks aft), and remove front screws.
Remove seat adjustment assist springs (manual seat).
Use vice grips to hold height adjust handle up, which will enable the height adjust rails to move on their tracks.
Align the rails so the middle screw and aft screws are accessible and remove them.
Remove lower frame rails, which will enable you to get to the middle screw of the upper frame rails.
Remove rear screws attaching top rail to black seat frame.
Align seat rails and remove 2 remaining screws on each rail.
Move clips holding seatbelt warning cable by grabbing tab with vicegrips.
Thread cable outside of seat frame.
Clean the dirty oil from 13mm wrench and remove 4 bolts holding the seatback to the bottom seat frame.
If you need to re-use your seat cushion & upholstery, the upholstery is held by its edges. [The edges have cardboard backing and are simply pressed into the seat frame edge.]
To remove the upholstery, spread a large towel on a clean workbench.
Put the seat on it, upholstery side down. This will expose the seat frame.
Press down on the seat. While pressing on the seat, start with a free edge, carefully lifting the edge part of the upholstery from the slots.
Installing the rails is the same, except that the slave side of the vertical adjustment lever. [There is a crossover linkage and the crossover linkage must lift the slave side up.]
Cinch down hard on the screws because the surface is now lubricated with seat track lubricant and that doesn't help secure the screws.
Insert the seatbelt rail before bolting the rear of the seat. [The shaped washer goes behind the plastic trim piece with the raised center facing the rail; the raised edge faces the drive tunnel. A rubber washer holds the bolt in place until secured.]
Finally, let me know if you complete this procedure successfully; it took a while to type this, and I'd appreciate knowing when each person has completed the repair! Please e-mail me at email@example.com
Richard Easley, Waco, Texas and Stu Ritter, Denver, Colorado.