How many miles are you getting between recommended service (mainly oil changes) with your Flexible Service System? I'm getting a lot and it worries me. Do you think there is something wrong with mine?

Here's the track record:
99 ML 320 purchased new in October 1999
Mix of city and highway driving. Average about 25K miles per year. The truck uses about a quart of oil every 4000 miles.

11865 miles A service - dino oil
23769 miles (11904 since last service) B service - dino oil
34299 miles (10530 since last service) A service - synthetic oil
47948 miles (13649 since last service) B service - synthetic oil
67329 miles (19381 since last service) B service - synthetic oil
86914 miles (19585 since last service) B service - synthetic oil
104XXX miles (17XXX since last service) B service - synthetic oil

I wouldn't go this many miles on purpose, but my wife drives the truck and she pays attention to the FSS as I asked her to. I'll take responsibility for not paying enough attention to the elapsed miles since the last service. Since Mercedes promoted this feature by telling me I would get between 10000 and 20000 miles between recommended service, I don't see that I've been negligent in maintaining the truck.