I once had a new S500 service loaner, I think it was a '95, and it had a rain sensor. It loks like a little lens on the back of the mirror assembly on the glass.

Why don't you just ask your dealer about it? And ask who does their glass work. This has to be an insurance job, anyway. BTW, my C320's windshield was replaced with a non-MB PPG glass last summer and the rain sensor works fine. It's part of the glass.

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Roger E.