well captain, I would say that if you get 1:1 with the steering wheel to tire movement, it means that the gearbox is OK, do not adjust it because it can make things worse.
I think (in order of highest probability) you need to check: front subframe mounts, idler arm bushings, lower ball joints or any ball joints in the steering linkages.

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MB 350 SL 2.8 -72
MB E220 -95
MB 230 E -82
MB 450 SEL -80 (project)