Typical problem. Do a search and you will find the instructions on how to fix it. There is a press fitted gear on a shaft that comes loose. You must take the shaft out, rough up the shaft and push the gear back on. Requires some finesse and a drill bit the size of the shaft to hold the odometer together while you take the shaft out, but it is a pretty simple repair.
I guess there is always the possiblity that the cable broke. Does the speedometer work?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13