Is it just the backgear layshaft that's damaged? It's a fairly simple job if so. MKI or MKII?
It's a complete strip down of the head in that case. The layshaft is easy to remove, the spindle will require a bit more effort. The bearings are usually a tight fit and will need drifting out, or you can contrive some sort of puller with studding and tube, or use a press if you're lucky enough to have access to one.
It's a good time to replace your belt if you've still got the original V-belt fitted.
I found the spindle came out of my model A with a few light taps from a rubber mallet once the locking rings were off. The trickier part is putting it back together because you have to thread the spindle through the various spacer, gears and pulleys in the right order whilst holding them inside the headstock - fiddly but doable.
Yes, that's right, it comes out the chuck end.
Shame about the missing teeth - it beggars belief the way some of these machines have been treated in the past! I had 9 out of 16 teeth missing on one of my screwcutting gearbox gears - someone obviously thought it was ok to change feed speeds whilst the lathe was running.
I presume you have access to the boxford parts list which was a great help in my rebuild. Here's a picture of all the parts, cleaned and re-painted before reassembly - James May eat your heart out! If you look closely you can see I never managed to take the front taper bearing off the spindle - it was tight and I was too worried about damaging it.
Good luck!
View attachment 103717
I don't know whether or not you're aware of it, but Tony at Lathes.co.uk does replacement gears for these. You machine the broken teeth off and either shrink or loctite the new gears in place. That way you'll have a spare set for the next time
What's the rear like? If the front is OK I'm assuming it is too.
Correct. Why would you not take it out and clean it?