Originally Posted by Idaho
I don't recommend going 9K miles between oil changes even with synthetic oil if you're planning keeping the car. Oil is the life blood of your car and the longer it is in your car the more contaminates it becomes exposed to and those contaminates in the oil will only accelerate your engine wear. If you're planning on keeping the car for the long run change the oil more frequently, but if you in a lease and don't plan on keeping the car past the lease then of course use the FSS.
No offense, but the engineers at Mercedes-Benz know a helluva lot more about oil & engines than anyone here on this forum, and I tend to trust their recommendations. If you'll read the post above, you'll notice the FSS takes a lot of things into account when it calculates miles remaining before the oil change, so sometimes it will be more or less than the recommended 6,000 mile interval. Either way I'll venture to bet that its calculations are on the conservative side.
Unless you can provide some documented proof that going 9k between oil changes is harmful I would suggest that you don't believe the hype. I say that because the whole concept of the "every 3,000 miles" oil change was developed by the guys that want to sell you oil and filters, not the manufacturer of the car/engine.
The manufacturing tolerances of modern engines are so much tighter than in the past that much less blow-by and contaminants get into the oil, and so the interval between changes can be longer.