Nix,
I am pretty certain that the "springs" are unique to the 113. FYI the seat construction is a "basket" of spring steel; over the springs, a "horsehair" pad is installed; and then the 'tex or leather cover is over this.
Particularly on the driver's side, what happens over time is that the horsehair pad begins to break down. I think this would be more so on the original (probably organic) then on a replacement which probably has more synthetic and thus longer-lasting products in its makeup. Second to this, the spring steel begins to break down--actually breaking. I've seen these broken and some shops just repair by brazing some new steel in place.
There's a well known albeit unorthodox "quick fix" and that is to stuff what we call "pool noodles" in the basket. I've seen this done on an old 240D and it really firmed up the seat.
To do the job properly, what you want to do is remove the seat from the car; remove the 'tex or leather seat cover. At this point you can assess the damage or condition to the pads; you may choose to replace them if not up to snuff. Remove them, and you'll see the spring basket. On the driver's side, don't be surprised to find broken steel.
Any good automotive upholstery shop should be able to replace parts of the steel; they completely rebuild seats for a lot of cars considerably more rare then our beloved 113. Using lengths of spring steel they can either augment what's there, or replace entirely. This isn't rocket science it's basic upholstery.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored
