Can you see the adjusting screw/locknut? I think it's a 6mm allen and a 3/4" nut, or metric equivalent. The problem is access.
The factory manual for my SL shows a wierd, twisted allen wrench and box end wrench that appears to be fitted to the adjuster and locknut from below.
I have verified that I can reach the allen socket from above with extensions and a flex-end, through the exhaust manifold between cylinders 7 and 8, and turn the locknut from below with a stubby end wrench (on th SL). You may be luckier with your 560SEL.
This is theory, though, as the car isn't yet on the road again after I did a steering gearbox overhaul. I'm praying I won't have to adjust it.

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1986 560SL
2002 Toyota Camry
1993 Lexus