The w126 odometer is different. Mine stopped last year after clicking for a couple of months. Took it out, looked at it. Spun one of the accessible gears by hand... it was stiff, sprayed some oil in there (WD40? can't remember). Spun gears by hand some more... became easier to spin, and put it back in. Worked fine since, but now making clicking noises again. But now I know the fix.

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Rob
'84 300SD 258K
'85 300D (sold)