Today I bit the bullet and ordered all the rear subframe linkage for my 87 300D, which is pretty much just decrepit back there at this point. Other than the swaybar, sway links and shocks, everything is original, and it's time for the next round. I'm also planning on swapping out the subframe itself for one I got from an 88 300E ... mine has a crack under the diff (which can probably be welded, but I have this nice frame in my shed so might as well use it).
The only thing I didn't order was springs ... they don't look bad and I'm not sure how to assess whether they ought to be replaced, too. One thing I can tell you is my car lilts to the right in the rear ... perceivably. Is that likely because of the worn linkage, or should I consider it a sign the springs are in need of replacement as well? To be honest, I'm not entirely sure the physics or what holds what up, beyond the basics.
I don't want to finish the job and have it still lilt because I left worn springs in there, but I also don't want to throw out perfectly good springs. Thoughts would be appreciated.
I won't start this project for a couple weeks at least, so take your time. I also might wimp out and take it to my indy ...

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)