I just fixed mine last week. Car had 297000 and the odo's stopped clocking miles.

Using the DieselGiant guide I got it apart and easily detemined that the grey colored potmetal gear that is first on the shaft was the culprit.

But I have a few notes that someone might want to consider:

1. The idea is to get the grey gear to bind onto the shaft.
DieselGiant says to use loctite down on the shaft.
I roughed the shaft with a file, but also put some JB weld into
gear hole and then reamed it out to create a press fit on the shaft.
2. To get the gear out I used a drill bit to hold all the number gears,
following in as I removed the long metal shaft so they did not all fall out.
Hope that makes sense.
3. I did have to remove one end of the shaft that had the small toothed
gears that click over the next higher wheel. (To create room to get out the grey wheel).

Small jewelers screwdriver set helped (got it at the dollar store).
Patience, patience. I did the job over two days.
Slip joint pliers helped as I pressed each shaft out and back in.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250