pokapotato

I just saw a small leak under the truck. The leak appears to be coming from the left rear of the cylinder block, running down to the pan and off the bottom of the bell housing. The leak appears to be originating from a small odd shaped plug/cover with a bolt in it, almost behind the starting motor. I am assuming that this cover is the rear block off for the oil galley in the cylinder block but I could be way off. Can anyone help here. It does not appear to coming from a high place such as the valve cover gasket.