Randall, apply a coat of Meguiar's Cleaner Wax to the windshield and see if that helps. After applying, rain should blow off the windshield while driving lessening the need for the wipers.

I've read several posts where owners experienced smearing with Rain-X so I would avoid anything associated with that name.

What brand wiper blade are you using? The older MB automobiles used Bosch wiper blades, not sure what MB specifies for the newer models.

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Fred Hoelzle