I suggest you pull the housing and inspect the main ring that seals the housing to the block and make sure there is no oil migrating down the block. Oil swells the rubber and will eventually break the housing. I would also suggest changing the sensor o-ring, on top, to viton while you are at it. I would get about two years before I would get a leak with the oem rubber o-rings, but it's been over 3 since I replaced them with the viton type.
It's also a great opertunity to do a flush.
Tuxedo Black 2014 Focus ST3
CD Silver 02 SVTF, #1336 - R.I.P.
"Brace for the G's, and fast heel-toe work!"- Hunter S. Thompson