I too own an '87 TD. Your problem is common actually with all 124s and 126s. The suspenion rubber gets old and worn and the rear wheels do sort of a tilt. My 87 has the same thing, though I haven't worn out the tires. I am keeping up on the tire rotations. The rear suspension of the 124s is a multi-link design, with several rubber bushing pivot points. With time they wear. I have seen many 126s going down the road with the rear wheels tilting inwards at the top.
If there was a problem with your self leveling system, usually it's seen by the car's back end sagging.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member