I second Bills answer. I didn't tear mine down completely. Someone prior to me had worked on them before. The transmission and transfer case worked perfectly before I took the Willys apart, but is did leak almost everywhere. I opened them up, inspected the shafts and gears for wear (none found), cleaned all surfaces, replaced all the gaskets and seals, then put it back together and painted. I did replace the clutch while I had the transmission off.
Bottom line, do what Bill suggests. The online information is incredibly detailed and free. I got lucky and didn't have to go in too deep. Hopefully, mine still works. I haven't driven it for a year. Tub is back on and I plan on taking it for a test spin this weekend.
Tim