HA! I love this topic. My 98 C Class has the FSS. MB tells me my warranty is NOT void if I do my own oil changes. I have closely monitored the oil color, and when mine triggered at 12,400 initially, the oil was nearly black, and was significantly dirtier than I would Ever allow from my own experience. I change now at color change, which although admittedly not a chemical test, is arguably a good qualifier for contaminanats in the oil. I do mine now at 5K, and reset the FSS myself when it goes. My brother has a 99 C280, and was "thrilled" to pay $225 for his service at first FSS trigger. Hmmmm. I have believed for a long time that clean oil and properly maintained coolant do the absolute most of any maintenenance factors. Of course you could change too often....but then oil is pretty cheap. 5-6K is a good balance in my view.