Do you check the transfer box oil when you check the OD? If you get the levels in the transferbox and OD correct, then check again after using them both, if the transfer box is overflowing from the filler hole, I think that gives you an answer? Otherwise, unless there is an external leak (which I am sure you will notice) there is nowhere else for the oil to go. Unless its overfilled, the OD wont chuck oil out of the breather in my experience.
Mine has been losing oil to the transferbox recently - its minimal and because of time I just top it up, but the other week, the OD was overflowing as it seems to have started drawing oil from the transferbox. I will take it all off over Christmas and replace the two face:face seals and the orange sealed bearing and it should all be fine again for another 100k miles.