The best tutorial for rebuilding the gearbox is on youtube, the guy does each section in short easy to follow stages.
Now....having said that I made two common mistakes -
1) On the end of the shift rail there should be a thimble cup that stops the oil leaking into the bellhousing and its often overlooked. I bought mine 2 years before and forgot to fit it. Dallas do a mod that keeps it held in place.
2) To stop oil leaking into the handbrake you can I'm told use a sealant behind the rear gear of the gearbox, I didnt do this either.
So my box will be dropped in the coimng months to do theres, frustrating but a necessity.