On the back side of the rear differential, facing the bumper, there is a plastic round plug that is 1.5 to 2 inches in diameter. There is an oil stain coming from this plug running down the differential to its base

. I had just noticed in about a week ago. Since I have the need to purchase a couple of things from the dealer I was going to look into replacing this plug. However, in the 2006 service manual there is no picture or discussion regarding this plug. I am stumped. Has anybody else come across this same concern or who has replaced this plug in the past and willing to share its part number? I can only imagine what may occur, if a slow leak is occuring, to the differential if left to be forgotten

, Thanks to all who look into this post and whom choose to reply.
Peace,
Scott