Have you looked at the small metal plate that captures the gear to drive it? It's pressed onto the shaft and if it comes loose, only has to move outward just a small amount in order to fail.
That plate has 4 tabs that insert into the gear cavities and hold the bump stops. Those fingers can also break off.
We commonly look at the large gear for indications of stripping,
But if you might have one of the early Generation 1 motors, it may have a second plastic gear that can strip.
And finally, if your motor has previously been rebuilt using plastic gears, it may have gotten aftermarket gears that were undersize, allowing only a small part of the edge of the teeth to engage. If the gear strips, it isn't as obvious as the picture above, and would require very close inspection of the very edges of the gear. Though some of those gears were white, many of the aftermarket gears were black.