The upper gearbox has proved troublesome, getting water in the top, where there is no seal. The water sinks to the bottom of the box and wrecks the seal on the output shaft and damages the bearing above the seal. Oil and water then go from the upper box into the lower main box. The main box becomes overfilled with oil. The upper gearbox runs dry and becomes noisy. The upper gearbox may be removed with the main body and pinion gear remaining in place. (Link to Gearbox manual.)