I was wrong (again) and I was not losing oil, the leakage was only the coolant but these days the coolant also contains lubricant so the oily residue I was looking at was what was left after the rest had evaporated.
Due to the complex cooling systems on this vehicle it required a lot dismantling, including the intake which then exposes how bad carbon build up might be.
Suffice to say the job is finished I may have some pictures of the valve intake stems to look at.
The costs are a mildly eye-watering $1300 but I guess it could have been worse.
I'll post pictures if I can.
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