Oil/mayo in coolant?

I have a friend with a 1.8. He has a small amount of mayo/oil on the header tank filler cap. It uses no oil or coolant, temps are normal, oil is clean, no mayo in cam cover or on dipstick and no steaming from oil filler when running or from exhaust?



Suggestions please?

from the last news http://ift.tt/1AcwqdQ

via IFTTT