I don't have an M60, but from your pics it appears that the oil is originating from the perimeter of head cover gasket, not the 'rings' that seal around the plug holes. In order to check if the 'rings' are leaking, you will need to pull the plugs and look down the holes. It is leaking in this area that may cause damage (unless the oil we see is able to make its way down the plug holes). But again, take this with a grain of salt as I'm much more familiar with the M50.
Dave