For a minute there I thought Rob had fired up his old valve based crystal ball!

If you do an internet search on "oil in coolant" you will find many car brands and examples of radiator failure particularly in cars 8-15 years of age with alloy radiators. I recently saw one example of a GM Astra which had the dealer looking in the wrong place some some time, the search solved the problem straight away.

all the best for Christmas!