Spoken like someone who has been there, done that and has the comemerative T-shirt! 
My vehicle is parked out at the parents place, as I don't have room for it in town. Sometimes people are out there using the arena for horses (We have a cross country course and such in the back) and they like to bring the kids. The kids see the cool 4 wheeler and go play on it. I come back and go to move it in the garage to work on it and find my Transfercase has somehow managed to find the mystical neutral and won't shift. So I pop it off, use a large screw driver to shift it back into a legal gear selection, and put it back together.
One of these days I need to just fix it so it doesn't do that. Or just keep yelling at parents to keep their kids off of my things. And my lawn! (Sheesh, I just turn 30 and I already feel old....

)
As for the right amount, one of those blue Chevron oil containers works great. But just to be sure I pull off the bolt from the side of the transfer case, then fill until oil starts coming out.
