If your gears come and go i would say youve blown the box? Jack it up, stick it in neutral and turn the back tyres, see if the tailshaft spins?
Replacing a snapped axle was one of the first of a long line of things i had to replace in my esky, but it gave me confidence etc to tackle any problem that came to hand. If youve got the time, patience give it a go yourself, and if you fail, then take it to a mechanic. thats only my personal opinion though.