Remove the square plug from the back of the knuckle and stick a zip tie in, like a dip stick. If there’s grease in the knuckle and oil in the diff, I’d drive it a little and see what happens.
In your 1st post there is a pic of the top plate. With the top plate removed, You should be able to push the shift forks around by hand, or drop in the shifter stalk and move it through the gear pattern. Can you do this? If you can’t, the problem is the top plate. That thing is very complicated...
Good to hear that you’re on the road to recovery. Another useful item for finding vacuum leaks is a can of non-flammable break cleaner. Spray it anywhere there could be a leak and if there is one, the rpm’s will decrease.
You are correct, it isn’t in my 60 and the case is bare. I got this with a bunch of other parts and I assumed it was a 60 plate. It was bound up and not shifting, so I took a bunch of pictures and dissembled it. I have all the rods, forks, shift head, balls, springs, interlock rollers, pins...
I have an h55f in my FJ60 but this top plate has the shifter neck on the other side. From the h55 shop manual, it looks like the case cover for an FJ/BJ40. Can anyone confirm this?
Again, I’ve only heard/read this, it could be urban legend. The chromoly axles are softer than stock which allows more twisting before they break. They will also wear out faster.
I’d start with the easiest fix which is a new drain plug. Honestly though I think there’s a problem with your oil pan. In a pinch I’ve replaced the drain plug without a gasket and it didn’t leak.