Mercedes source has a panphlet on how to replace padding and seat springs in 126/123 sedans. The orig. springs fail and the seat feels that of a truck floating unit. You can replace both pads for $125/a piece, and the seat bottom spring for 230$. Assuming your leather is still good and you know how to dismount the seat's upholstery, you can do this job yourself. Looking at about $500 per seat w/ all new parts. May be worth it if you got heated units and manual lumbar control as I do in my 380 sel. les