Just out of curiosity, is the gear that is failing in the
speedometer/odometer or transmission? I am trying to understand what is
failing and possible causes. Is there something that is binding that causes
the gear theeth to strip? Is there a worn bushing that is causing the gears
to not mesh properly?
In other (old school) speedos, there was a plastic gear in the transaxle
that drove the speedo flex cable and in turn screwed into the speedo
indicator on the instrument panel. I saw a few flex cables over the years
that were either worn or needed lube to keep them from making noise and
eventually binding that chewed up the plastic gear in the transaxle. Saw a
few speedometer units also in the instrument panel that the input shaft
started to stick and needed to be re-lubed. I never had to open up a speedo
unit to fix anything inside. If you do open one - be careful not to get any
iron debris inside. there is a very tight clearance between the iron bell
driven by the speedo cable and the driven magnet. Iron filings or any
ferromagnetic debris will get sucked into the magnet and mess things up.
I use automatic transmission fluid for all oiling. It doesn't gum up like
motor oil does.
   Oppie