Thanks for the replies, folks. I'll try cleaning first, then the wax. I'm pretty sure the blades are Bosch. I'll post back here in a week or two with results.

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2003 E320 wagon, ~80k, "Sputnik"
1987 300 SDL, ~160k, "The Pimp Daddy" (sold April 2010)
1984 300 TD, ~200k, "Das Boot" (Demised March 2008)