Thank you for your comments. Just to clarify this in my mind with the filler cap off there is a fair bit of windage from the pistons normally? I thought it was a block vent system because the valve cover has oil around the oil filler cap, and the air cleaner lid above the inlet for the pcv system looks like it's having air forced against it.
Shouldn't it be drawing air from there, and oil appears to be leaking from the rear of the engine, I was thinking that the rear main might be having oil forced out of it. Does that make any sense?