We depend on O-Rings for many pneumatic operations in our model airplanes.  In the case of the BVM O-Ring Brake System (US Patent #5,601,159) we count on this simple device to bring our jets to a safe stop.
Our most sophisticated competition scale jets like the F-100 and F-86, actually have 5 separate pneumatic systems to give us the required reliability for operating landing gear, doors, speed brakes, wheel brakes, canopy and tank drop.  Most o-rings are made from Buna rubber and do have a useful lifespan.

     If your cylinders or O-Ring brakes are over 5 years old and are experiencing leaks, first try to rejuvenate their function by injecting some BVM "Thin O-Ring" Lube and cycle the system.

     DO NOT use any other type of lube, especially a petroleum based substance like WD-40.  Doing so, will totally pollute that cylinder and possibly the entire pneumatic system attached to it.

     If the O-Rings in your BVM Brakes are malfunctioning, they are easily replaced with new pre-lubed O-Rings from BVM.  Use only a sharpened wood dowel to remove them from the brake hub.