...that I did the same job on my 1983 300SD when living in Encino, in the San Fernando Valley in the early 1990s. The spring had broken and the seat bolster leaned to the left when you sat on it, causing hellish pain in the sciatic (I think) nerve. Had some 90k on it at the time, including 45k from the first owner who may have been heavier than me.

I recall it as one of the toughest jobs I ever did as it was 100F at the time, the seat was hell to get out and very heavy and several small plastic trim pieces broke from age when I dismantled it to remove the old spring.

However, it had to be done and the new seat spring showed far stronger gussetting in the middle where the old one had broken. I seem to recall someone writing that all pre-1986 W126s (and earlier W116s?) are plagued with this bad design. Not sure of this but I believe the 1986 and later W126s use the new design. My 1990 W126 is fine at 103k in this regard.

I have over 100k on the replacement in the SD and it's fine. I weigh some 165 lbs, pretty much stable over the years.