THESE????
I didn't see this until now, sorry, but those aren't the gears that fail. They are in the gear train and spin freely on pins/ shafts. Because they aren't in constant tension as pressed axle gears are, they seldom fail, cracking from the continuous force of the press tension. What they
do sell and how I bought the few that I needed is the three axle wheel assembly with gears for the Plymouth. The gear is the same and the axle diameter is the same so they are direct replacement. I pulled the wheels out of the gears and had three gears. Two of those gave me three sets of gears for those four axle locos.
Additionally, for likely interchangeability, most Bachmann axles of the older era (and maybe newer) share the same axle size (and .3 mod tooth profile) so again, if the gear tooth count is the same and the offset is the same there's a good chance that they will be interchangeable. Hope that helps.