Leaking Tranny

If their are no threads in the hole, and nothing is hanging around looking like it belongs there, I'd suggest something along the lines of JB Weld to seal the hole. It's possible it threw something out the side of the case, but more likely that something hit it hard enough to knock a little hole in it. Transmission cases are commonly cast aluminum and all castings have weak spots in them. You would be supprised what a stray rock can do to it if it hits it just right.