Sorry it took so long, been having issues with my FTP programs, but things are running again.
Anyways, here is what I needed to do when my odometer stopped at the change from 99,999 to 100,000 miles. Seems to just be a weak mechanism that doesn't have a strong enough spring to push that last digit over. But if you get it all past that point, it clicks along normally once again (probably until the 200,000 mile mark).
Sorry I don't have the greatest photos of it, but most of the work is just disassembly and reassembly. The actual "fix" takes about 30 seconds or so. But a disclaimer, this is only what fixed MINE, but it may not fix yours if something else caused it to stop there.
Be gentle, don't touch anything you don't have to. Grab the wrong part the wrong way, and the speedometer portion will be ruined and need professional repair.
Here is the link