There is a big T55 plug/drain of some sort to the left (passenger side) of the oil drain tube on the front of the engine. I have a very slow oil leak coming from this plug, and before I pull it I'd like to know what exactly it's for and part of. There are no connectors, it's just a plug. My service manual mentions nothing about this plug so I'm kind of stumped, short of pulling it to find oil or coolant come out. It's above the oil pan, but not by much. Ideas?