You can just buy the little gear for the electric odometer motor. Yours is electronic. It is a $10 dollar part take the ic out and take it apart and replace it.
Worm Gear Ford | eBay

 

I'll check that out. Thank you for the link.

 

Ok been down this road before and have had the truck less than 2 months. Well its my sons truck. its 99 ranger xlt supercab 4wd automatic 4.o ohv.
That being said that his a 4wd matters what sensor controls speedo/odometer. If its 4wd like mine and neither speedo or odometer work then suspect abs sensor on rear end. But like the original poster stated his speedo worked fine. That was my thoughts if speedo works and odometer does not the problem is in the cluster. Yes these are all electric no cables.
After searching these forums and finding some very helpful information. I took cluster out fully expecting to find stripped gears or a bad motor that drives the odometer. What a found was this, gears where not stripped they where a okay. What was wrong was one of the clear plastic tabs that lock down the odometer motor was broken. This left the motor in the cluster on an angle only locked down on 1 side. The motor shell has a tab that extends out 1 on each side. These ears or tabs lock under the clear plastic tabs on the odometers shell. How we ended up fixing it was feeding a thin wire tie down though the odometer housing and back up cinching the motor in the correct position. Its has to be a narrow wire tie as not come in contact with any of the gears. I also put a dab of hot glue on wire where it looped over the ear on the motor. Redneck fix maybe but it worked. There are also you tube videos for fixing the gears if that's the problem as well how to take the cluster out. I am proud of my redneck fixes more so when they do not involve money. Oh by the way its been almost 3 weeks and odometer is still working fine after the fix.