727 Help Please. pics!

I am trying to narrow down a leak in my 727. It has a new aluminum pan with the new style gasket so i think we have ruled that out... I was under the car today, cleaned everything on the tranny that I could then drove it and got it all warmed up... After that i had it back in the air to watch for leaks. The picture below shows a core tranny that i had at my shop. It seems to me like it is something like a soft plug or something at the back passenger lower side. It looks like the tail housing has an ear that possibly keeps this piece from coming out. There is a little depression under this and it seems to hold a little fluid and then runs down on to the gasket and pan. In the core tranny it is set about an 1/8"... in mine it is flush out to the edge and seems to be resting on the ear of the tail shaft housing. Can i set mine back in place with a punch to stop the leaking and what is it?

Thank you,
Matt