If you have a local shop that you trust with changing your brakes, you'll definitely save some money there. I didn't change brakes yet on my C230, so not sure about prices yet, but when I changed brakes at my local shop vs dealer on my old E320, it was about 50% cheaper for the same brake pads. Not sure about the brake flush - I try to do get a brake flush done every 50,000 km.
On the 2008 C300, they recommend changing your brake fluid at 2 years.
At the time, there was a flurry of activity on another forum that supported following their recommendation.
As for brakes, on the C300, a MB tech that also frequents that forum recommended changing the rotars every second brake pad change and that the brake pad change was simple enough for a user to do it. I don't think I'd recommend that any user attempt it after all, it is what you rely on to stop the vehicle.
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