My '08 ML 320 CDI diesel is using oil.
 

Does anyone know why my '08 diesel, which I bought with 9,000 miles on it, uses oil? When we take a trip, driving on the interstate, after a few hundred miles, I get the warning to "check oil at next fill-up". I have to add 1/2 qt., and next day same thing again. However, I have driven as much as 1,800 miles without this happening. I usually have the cruise set at about 64 mph. Engine now has 17,000 miles. Dealer has said to watch it and see if it continues to happen. I don't think this is normal. Has anyone had the same problem with an '08 diesel?