If nothing turns out, don't ignore 104.992's suggestion about possible clogged cabin air filters being the cause of the problem.

I know you can take a peak at a very small area of the cabin filters, and estimate their condition without dismantling anything. I did this on my '95 E300D by lifting one of the rubber trims near the wiper arm, and looking behind it.

This however was awhile back, and can't remember which trim I lifted. If you are stuck, I can try it again, and let you know which trim to peak under.

Phil



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'95 E300 Diesel, 264,000 Miles. [Sold it]