Nice Mitch! Any chance you happened to count out the gear ratio while you were in there?
Another possible factor in the wear... most of the newer locos are geared much lower with a single-thread worm (as opposed to a triple-thread worm on a 736.) Don't get me wrong, the lower gear ratio and slower speeds are much preferred. Lionel could have gained back some longevity by using a steel worm, and a bronze (or brass) worm wheel.
Ten years is still a long time. Not a problem, as long as spare parts are available.