Greg, I'm with you. I change mine every 5-6K on all my cars and let MB do it under the service plan that came with my 2004 MB at 10K. I still use 0W-40 Mobil 1 in the '04 since it is under warranty but you can bet it will be 15W-50 once the warranty expires. I would be willing to bet that 0W is specified for EPA fuel mileage purposes only. Further, I could never understand a 0W-30 being specified for any vehicle that lives in the SE or SW, especially as a year 'round fill. I wonder if the 15W-50 Mobil 1 (now discontinued) contains more ZDDP and phosphorus (anti-wear agents which are being reduced or phased out courtesy of the EPA) than Ow-40, hence the non-approval by MB. I know that Mobil 1 10W-50 was/is available in Europe and approved by MB. For the average person, oil and filter changes every 5K are cheap enough to perform and a smart practice to ensure engine longevity. Mark