I'd have to second the voice of experience in this post:

"M.B.DOC
Moderator Join Date: Mar 1999
Location: Snellville, Ga USA
Posts: 5,397


Have the charging system checked..... WHILE the problem is there!
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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman ..."

I had almost the identical problem on my '86 190e which disappeared after changing the voltage regulator on the back of the alternator.

Happy trails...