Interesting. I can't find 0W-40 on Mobil's website, their tech line didn't know anything until I read them the letter, then they said it is only available in bulk to dealers. My dealer doesn't know anything about it and is using 10W-30. MBUSA's tech line knew absolutely nothing about to letter! Kuan, where do you get your info that 0W-40 will be available in stores soon? I can afford to wait a while if it will, but so far I can't fine any evidence of that. Perhaps I should just stick to mineral oil and continue changing at 5K as I have been. Also, I used synthetic in my 300TE (M103) and changed it every 3,750 miles. It seemed to make no difference whatsoever and I experienced all the usual M103 problems such as worn valve guides at the usual mileage.