FYI, brake fluid is hygroscopic, which means it absorbs water and water vapor, even more readily than does diesel fuel. It gets more acidic with time and eventually starts corroding and oxidizing the various internals of the braking system. Braking components can reach temperatures of 5000 degrees, yet brake fluid won't boil even at those temperatures. However, when a certain level of water is absorbed, it will precipitate out and will either boil, or turn to a gas. If you notice a brake fade, especially coming downhill, the water is boiling or the water vapor gas is being compressed (brake fluid, like all fluids, will not compress, but gases will). The water in the brake fluid can also create rust inside the brake system, leading to a failure of the brake wheel cylinders and calipers. Failing to change brake fluid at the recommended intervals can eventually result in catastrophic brake failure, which will require replacement of the entire braking system, including brake lines, calipers, the whole deal. Just something to think about.