Nobody pays much attention to the piston rod seal in the Aerostar (Mooney/Cirrus) Cleveland Brake Master Cylinder until it leaks. Even when it does leak it won't cause much more than carpet damage, unless you ignore it. When the OEM piston rod O-ring does need replacing due to wear causing leakage, that's the time to fix it once and for all. Like all Marsh Brothers products, our glands and seals are developed to last for the long haul. To learn more, visit www.MarshBrothersAviation.com or contact us at [email protected]