So I've got a '07 A6 also with the 4.2 and it's just started with coolant in the oil cap, but there's no chocolate milk on the dipstick yet. I'm wondering if the oil cooler fix stopped the contamination of the oil? You say you've gone another 40k miles, so I assume they're not mixing, you only have disappearing coolant. Did you ever have coolant in the oil?

 

Hi,

just read your post. I did have similar issues with coolant mixing with oil. First thing I did was to analyze the oil. Take the sample from the engine to be tested for presence of coolant. You will get confirmation if it is an internal leak and they find coolant in the oil. I had to redo pretty much everything related to the coolant lines. Mine was internal leak and the coolant was entering the engine through the back coolant pipes (on the back of the engine where the timing chain is).