Unfortunately, I don't believe there is a way to lock these in a direction by conventional means. You have to use TMCC to do so. I suppose it could also be done using Legacy.
I think the stripping has something to do with the angle at which the motor sets in the truck. I recollect reading something in the past that some Lionel engines had this problem and there was a way to shim the motor enough to prevent the gear from stripping. Someone more knowledgeable than I would have to explain that process though.
Curt