haasman-
I had the same annoying problem on my 190e. Turned out to be contact between the plastic of the steering wheel cover and the steering column cover.
Try this-
At the point where the steering wheel cover ends (right before the cruise control and turn signal stalks), pull up on the plastic (at the top) and then turn the steering wheel. If the sound is gone,
slide a small wedge to raise the plastic enough so that there is no more contact.
I hope this works for you - I owe you for your past help!

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1993 190e 2.3
Spruce Green Metallic
62k original