ck42,
From my experience, I would suspect the rear subframe mounts first, but also consider the slop may originate in the front guide rod mounts.

I had all these replaced in my C126s and it improved the ride in all aspects.

edit:
For those who struggled, as did I, with the terminology:
The "bearing bracket bushings" serve as the front subframe mounts (2 per side) and if you also hear knocking noises, the "guide rod mounts" may need replacement. All three rubber pieces (per side) assemble into the bearing bracket (aka brake strut mount).

Cheers, Andrew Seidel.

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