Initially, I was pleasantly surprised by the overall condition of the parts car's interior. The car had been sitting in a field for around 13 years, but the interior seemed to have held up pretty well. There were some tears in the driver's seat upholstery and the padding had flattened a bit. Overall, it was pretty nice. Plus, although I really like palomino upholstery, I took a shine to the older, slightly more rare bamboo colored interior from the '79. So, to help recover a bit of cash, I sold the leather interior and opted to use the '79 interior. A little later on, I even sold the decent passenger seat out of the '83. At that point, I was committed.
My initial reaction when I started working on the '79 seats was that I'd made a mistake. All the hardware was rusted, which made disassembly difficult. I worked at it bit by bit, and last weekend, I finally finished rebuilding the driver's seat from the '79. I repaired the seat springs, added some new springs for reinforcement, added a layer of canvas between the spring frame and the padding, and replaced the dried out, crumbling old horsehair padding with new memory foam. Considering how much I'd compromised on the materials (as opposed to using brand new Mercedes OEM parts), I think the end result is really nice, and feels very comfortable after a test-sit.
I still need to rebuild the passenger seat and the rear seat. Thankfully, all this work in the basement is keeping me from having to work outside in the cold. Of course, once the seats are done, I'll be back to doing bodywork on the '83 shell.
Here's a Youtube series I did showing what I did to rebuild the driver's seat: