I had a similar problem with mine and took the circuit board out, cleaned it with contact cleaner, re-flowed all of the large solder joints (avoiding the smaller surface mounted components), and re-assembled using dielectric grease on all the connectors. After that it worked like new again. Some Googling led me to a post on another discussion board that had a pictorial. Check it out here- If your antenna stops moving - Benzworld.org - Mercedes-Benz Discussion Forum

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'82 300D - Light Ivory, 2nd Owner (Back in the wind April 2013!)

'95 E300D - White, grey interior. (Suffering from stuck/broken glow plugs)

Deuteronomy 22:4-
"Thou shalt not see thy brother's ass or his ox fall down by the way, and hide thyself from them: thou shalt surely help him to lift them up again."