Didn't realize it wasn't a blind hole, my bad. I looked at mine and thought it was a blind hole, just drilled longer then the rest. I will have a closer look to be sure. It may be as Soundguy says, a hole in the bellhousing to let a mainseal leak drip out. I have never seen a hole this big for that purpose however. Usually just a small slit or hole to let oil out and not let debris in.