the drive wheel/gear coming loose is sort of common (to me anyways).
You need to pop-off the cover with "pointy object" and retighten the screw. The drivers side seems to work loose on my Tiger and Panther after a while.
Only seems to happen on my older,non S/S tanks though.try a little thread lock.
Be careful when flipping the barrel......you might do damage to the fragile wires inside(poor solder joints)