As described in post 26, I had a problem with steering not centering. It was caused by the idler arm bearing.

Did you replace the idler arm bearing kit? If so, was it replaced with at OE Mercedes kit or an aftermarket kit, like Lemfoerder or Uro or ?? I had put in a new Lemfoerder in my W123 and it was the cause of the problem. I replaced it with an OE kit and problem was solved. I could explain why. But first check what you have in there.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I did see that, Meyle was all I could get earlier this year, however it looks like OEM is now available so might try that. I did check them and not seeing any issue but its an easy swap of those so might give it a shot.

Only 4 idler bushings left in Germany, for $40 I'll give the OEM one a shot.

Might as well get them while you can.

You could jack car up and watch while someone turns the wheel. The rubber inserts should not move in the chassis tube. For my cars, manual say there should be about 0.5mm end to end slack in pivot after idler bolt is fully torqued. In other words, bushing should not restrict movement.

This may not be your problem, but it is a cheap fix if it is!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I did that but didn't check for bushing movement, I really wasnt a fan of the Meyle, first set came apart just trying to install so happy to swap to OEM.

I have a quick ratio Cosworth steering box getting refreshed at the moment so thats going to be going in regardless, but wasn't sure if there's anything else to check. Honestly I've replaced every bit of rubber in the suspension so I doubt it.