I have exactly the same issue with my 1993 190E 2.6, have been unable to find the problem so far. The bowden cable theory is interesting, I was thinking vacuum perhaps but who knows. Might even be a torn mount under the car or suspension issue. Least likely I think would be a worn out differential. Until something lets go I suppose I may never know. I already looked at it myself and had 2 independents try to assess it to no avail.

__________________
'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)