Above mentioned fix is for the W210 chassis from original post, a dealer mod for sure. If your W124 chassis is doing this I'll bet it's the regulator.

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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V