The cockeyed steering wheel is probably because when the front wheels were aligned the tech didn't set the steering wheel straight. Someone familiar with MBZ alignments should be able to realign the front end with the wheel set straight. The steering box is an easy fix if you still have play after eliminating most other causes. There are several threads on the topic, just do it 1/8 to 1/4 turn at a time and DON'T over tighten. As to the coupling, I doubt that is the source of your play but if it is not in good shape you probably ought to replace it.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold