91 W250 Cummins-Odometer stopped working

The speedo still works fine, both odometers quit working last week.Is there any way to rebuild or repair? Where would I get parts? I've looked online a
bunch of places but everybody seems to want to sell aftermarket replacement speedometer.TIA for your help.
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there
a
replacement
Hope I'm not steering you wrong here. My 92 W250 is a gas V8. It has the same speedometer as my 90 D150. They are electronic. No cable to the transmission. If the odometer works at least the speed sensor (on the transmission or transfer case if 4X4) is working.
Al
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The odometers are what stopped working, the speedometer still works. Thats why I think it is something internal to the guage, but maybe the sensor for the odometer is somewhere else? I really don't know.

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