what you'll find is broken pieces, if you disassemble it far enough and look closely, in which case ... you'll break it further
there are no "repro odometers" Larry, and there is a reason why the shop manual doesn't bother to detail repairs
the number wheels have little plastic tabs on the sides that bump into the tab on the next wheel once each revolution - when the mechanism gets gummed up it takes too much force to push the next wheel and the plastic tab breaks .... not fixable
if you can find another speedo head, replaceing the whole thing is your best bet
Bill