[fox46]

After a second look at that picture, I've noticed if you have that drive sprocket in the picture on the shaft and that nylon spacer is too long, when you tighten the bolt in the end of the shaft it will put a compressive force on that sprocket. The result will be that the bolt in the end of the shaft will be pulling the hex out of the transmission almost like a gear puller. This could certainly break any adhesive bonds and pull the hex stub shaft out of its press fit. Make sure you have the appropriate sized spacers on the end of that hex shaft and leave some space - like 0.010" for the drive gear to slide back and forth to ensure you do not put any tension on the stub shaft and pull it out of the bore.