When it comes to your vehicle’s brake fluid, consult your car’s owner’s manual to see what the manufacturer recommends. You may also want to discuss the subject of brake fluid with a trusted mechanic if the manufacturer doesn’t give any guidance. Don’t be surprised if a mechanic suggests replacing the brake fluid periodically, because mechanics probably have seen what can happen if you don’t.
What can happen? Even though brake fluid dwells in a sealed system it still can absorb moisture over time, and that can lead to corrosion in the brake system. Moisture also lowers the boiling temperature of brake fluid, and that can reduce braking effectiveness in repeated hard stops.