Perhaps the dash speedo display is like the one in my 1965 Chrysler, which has a spinning magnet inside an aluminum cup. The needle is attached to the cup. The magnet shaft had worn in the bare aluminum bore to wobble and make the needle dance. When bad, the magnet grabs the cup to hopefully just break the cable. I sent the guts to a speedo shop in Bakersfield, CA which re-bored it and pressed in a bronze bushing. That was ~1993 so unlikely still there. My 1982 Dodge had a similar issue with its spinning magnet, but a plastic part had cracked to allow wobble, which I fixed by wrapping strong thread w/ epoxy. I haven't dug into my M-B speedo, but if similar such might be the issue and fixes. Of course in modern cars, the speedo needle is just a motorized display driven by a body computer.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans