I had an 82 300SD and bought a new set of seats on ebay from a 1986 car. They fit perfectly, except that I needed to swap the seat belt holders from the old seats and put on the new ones. Huge difference, but probably not as much as a new seat frame would make. But the upholstery on my old seats was shot, too.

- Ted

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1987 300SDL 265,000 mi.
1982 300SD 325,000 mi. (and holding)
1956 Packard Clipper 150,000 mi.