Really now? Never heard of that one. Kind of reminds me of the stories of muffler bearings, and changing out the air in the tires. If there is any kind of problem with the brake fluid that would warrant a change that early, then IMO Chevy/GM needs to eat that cost. Brake fluid usually lasts for decades under normal use, a good change interval might be 100K miles if you are worried about moisture in the lines. If you drive on the ragged edge in hot dusty conditions, and normally hop out of your Sonic with the brake rotors glowing red hot, then that might dictate a more frequent fluid change, but something tells me you don't drive it that hard. lol