none of the cogs were shorn and i did not need to remove the dial and facia plate.
the main odo had "derailed" from its normal position, and I was able to jiggle it back into position. I expect that by resetting the trip odometer whilst the car was moving, the odo derailed rather than shearing the gear. a much easier fix.
thanks for all the inputs from past posts on instrument cluster removal and odo-broken theories.