Kwikee doesn't make their own motors and the step motor is just a common automotive part, usually a motor designed for a power window mechanism. Since pennies count when an item is bought by the 10's of thousands, I suspect the plastic gear was a cost reduction measure. You might be able to find another motor that fits the same mounts but more rugged construction. Try taking the motor to a NAPA store and see if they can find one that is similar.
But I wonder why yours failed? There shouldn't be much of any load on the motor unless your steps mechanical mechanism is binding, and even then the motor usually just stops well short of any gear damage. The step controller is supposed to have a current limiting mechanism so that the step stops if it bumps into something, or if somebody is standing on it when it tries to move.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL