We went by FSS for the first 4 years, and then we picked up a warranty that requires us to change at 5000 miles. 3k, 5k, 12k??? Who knows. Synthetic doesn't break down like dino does, but they both pick up combustion contaminants that the filter can't get rid of. MB has an 8 quart capacity, so the ratio of contamination to oil should be better than a 5 quart car. Who's to say how effective that logic is?