Actually, I found that it may be possible to open the gearbox. I replaced one recently, and the new one shows that there are 3 small hex screws, two about across from the shaft, and one at the bottom end. On my original gearbox, they are covered with something like black paint that might be able to be removed. If the screws aren't covered, they are very easy to remove and disassemble the gearbox. It's not hard to reassemble. In fact, I tried swapping out parts from my old and new gearboxes to see which combination worked best, but I settled for just using the new one.
-Joe
