Small update: some more info today. Not conclusive but a step in the right direction. A mate's brother in law is a mechanic and so we put the car on his hoist today and poked around with the inspection camera for a while. Definitely lots of oil around the head gasket, however we DID find some oil up higher leaking around the inlet manifold. So I'm hoping that the rocker cover is leaking, running either side of an intake runner on the manifold and then settling a bit where the head gasket stocks out and spreading from there. Still might be both! I've got a minor leak on the other side above the power steering pump from the rocker cover gasket and I wouldn't mind painting my rocker cover, so I reckon I'll tackle that, clean everything up and see what happens. Only costs me a rocker cover gasket to try. Unfortunately we also saw the rear main was leaking. That was replaced earlier this year so should be a warranty job but have to go back to someone and break the news that they have to remove and refit the transmission for no charge.