We recommend flushing fluids when they get dark or reach a certain age. Generally, fluids last for about two years with some exceptions. When the brake fluid is dark that means there is debris suspended in the fluid and possibly moisture, too. Over time, debris will wear-out seals inside the master cylinder, ABS control module, and calipers causing leaks and or ABS problems. Moisture in the brake fluid causes brake fade. Flushing the power steering and cooling systems is done for similar reasons.