There is a 15 year old service bulletin on that problem, requires replacement of the front section of the parking brake cable!
The W124 & W126 chassis from 1986 thru 1989 were affected.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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