Replacing a clutch, before we started i noticed the tiniest wet patch of oil at the bottom of the engine / bellhousing the size of a 50 cent piece.
We get the flywheel off and of course find this:

Is it for sure the rear main, or are these engines known to have sump gasket problems around the seal holder assembly?
Has anyone ever replaced a rear main using a self tapping screw extraction method? I really don't want to remove the seal holder as doing so (if it can even be done without removing the sump) looks like it would really perturb the sump gasket.