Brake fluid is very hydroscopic which means it attracts and absorbs moisture. This is a natural occurrence in all brake systems. Contrary to popular belief, there is no such thing as a sealed system. Because brake fluid attracts water like a magnet attracts metal, moisture can even be drawn into the fluid through the pores of a rubber brake system components. Moisture in the brake system combines with available oxygen to form oxidation therefore damaging vital braking components. To maintain a safe braking system a flush is recommended every two years.