anyway back to the picture, you can see the oil starts from the middle of that rear sensor, the mounting face is pretty far back from there. Not that that means anything though, oil leaks can behave in mysterious ways

but that would be my 1st step, replace that sensor and clean up the housing as best ya can, see if it comes back and from where.
Lot of yorkshire folk on here living down south, myself included. Its where the good money is
