Originally Posted By: ChrisD46
... Buick dealer told me GM uses a "closed" brake system so moisture isn't a problem, brake fluid should be replenished but doesn't need to be bled and replaced . Does this sound correct?
No, they are not closed system in the sense that moisture can't get to the fluid. There are seals at every wheel that allows for movement and separates the brake fluid from the environment. Unfortunately, this only minimizes the contact between brake fluid and the environment, but does not completely eliminate it. It is at these seals where fluid contamination is the greastest. That's why I butter the bore surfaces with silicone grease, to exclude the environment from reaching the fluid.