You can see the hole in the output shaft in this photo.
But I noticed the gearbox was loose and decided to try to fix it. I had to remove 3 sets of gears to allow me to get to the 3 screws that hold the case and motor together. These screws got locktite.
https://picasaweb.google.com/1064737...85071549820722
https://picasaweb.google.com/1064737...85957591941298