No clue why it is missing. It looks like the previous owner redid some of the seals. Not sure if it was pulled or not. It doesnt leak when it is sitting, but definitely does when driving. If its not the bolt, then its the input shaft seal.
My hope is that once a bolt is put in there, the vibrations will stop, and so will the leaking. Otherwise, im going to pickup a used tcase and put it in because i believe you have to pull the tcase to change the input shaft seal, so might as well just replace it with one with less miles.