"My mechanic says the gear in the lower unit and the gear up top do not match and should have the same part number because they are sold as a unit and that is why the driveshaft broke. He said the driveshaft was spinning in the top and when it caught it snapped the driveshaft, and that the bearing had gotten very hot. He says once he replaces the two gears and bearing all should be fine. What do you think?"