Old lawn tractor trans jammed. I took case apart and all the teeth on 1 gear were extremely worn. Actually down to a razor edge. The opposing gear looked perfect. I did some digging and found a new gear at dealer and figured $70 was worth it to make mower function. Is it normal for 1 gear to wear a lot and the opposite gear to look ok? I would expct both gears to be worn. Perhaps the heat treating on 1 of the gears was off?