Seat belts - don't know if the retracting mechanism is rebuildable but it is easier to replace a high-mileage specimen with anemic pull with a low mileage less tugged at one with more spring left in it.

VCVs for the diesels - NLA. Buy the warranty, test it on your car, take it back if shot. Also vacuum pump - the rebuild kit appears NLA for the 617. Also the central lock vacuum pump. Buy warranty, swap into your car to test, return if bad.

ABS wheel speed sensor can be bought new for w126 front left north of $200 front right around $150. Much cheaper at the yard - bring multimeter to test Ω and V.

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'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.