"The coolant service for my SL is every 3 years, per my manual and the dealer FSS. 15 years for coolant is asinine."

I also think 15-year coolant change interval is a bit of a stretch. Re-reading the booklet again (MY2004), the story is excerpted below...

1. A-Service: fluid level check for: windshield washer, brake, and battery.

2. B-Service: fluid level check for: windshield washer, brake, battery, power steering, and coolant.

3. Additional Work to be Performed together with the Respective Service:
- replace brake fluid every 2 years
- replace coolant every 250,000 km or 15 years, for C, S, SLK, CLK, SL, and CL; also for 'low temperature circuit' for S600, CL600, and SL600
- replace coolant every 3 years for 'main circuit' for S600, CL600, and SL600
- (note, no mention of transmission and power steering fluid change interval)


Back to coolant... I guess for the V12s, the schedule is 3-year for 'main circuit' and 15-year for 'low temperature circuit' (but I have no idea what these circuits mean). And for other class/models, it's 15 years across the board!