I ended up buying one of those lumbar pillows, and that made a difference. But it still feels weird to drive it. My middle back gets tight.

It could be my shoes are shot, but I drove my mercedes for about a week and didn't have this issue.

I do have the seat from my 93 (I'm parting it out. wasn't worth selling) that I might check to see what it looks like (since I KNOW it worked fine). I don't know the size of the person who drove it before me (for the bulk of the mileage). it was a father/son combo who drove it up here, but I don't know if the main driver (prior to the son) was the mom, and I have no idea of her size. But I do know the father and the so were both skinny.

I'm glad to hear it's not significantly different from the 240's. I repaired my 240 lumbar support about 900 times.

(In the process of dealing with this, I think I found out my AC compressor doesn't work at all. not sure if it's the clutch or switch. I tried filling it up with freon, but nothing changed in the system. It just doesn't turn on. That along with the lumbar issue is making it not so much fun to drive the car.)
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1985 245. 246K Gone..but not forgotten. Sold in 2013, found 2018! Still running on the road. Of course.