The gear box is the hardest thing to work on, of course mine was stuck because the oil dried up and everything got stuck and the taper pins were facing the wrong way to knock out so I had to spend extra time to do a teardown. Keep in mind that the levers on the gear box are right and lefts so make sure you try all gear selections before installing on lathe. I did know this and still got them reversed, but can be redone easily when off the lathe. Turn the side oilers on the head stock so you can put a piece of wire thru the hole to hold the spring loaded oilers down when installing spindle. Take off your gear selection chart so you don't lose the finish and if you do there is someone who can make a new one for you out there if you do want the lathe to look nice. The missing tooth can be fixed with some welding and filing and some other ways also, just needed to fill the gap so the next tooth does not come off. You could leave it go if you do not plan on using backgear that ofter.Good luck.
Paul