I just discovered yesterday i have an oil leak

there is a plastic thing that is between my motor and transmission, bolts to my tranny and has a hole in the bottom... it covers the flywheel.... is it a flywheel cover??? anyways... i got oil leaking out of that hole... hope its nothing too serious... its been sitting for a few years till a few weeks ago when gpa gave to me...runs good other than this... hope its not a rear main seal

what else could it be? its not the oil pan or tranny pan gaskets....