If the brake pads and rotors are changed, is it necessary to flush out the brake fluid as well? The reason I ask is that my dealer changed the front pads and rotors about a year ago and on the detailed invoice do not mention anything about changing the brake fluid. And if I flush out the brake fluid myself NOW, would it have to be flushed out again if I need to change my brake pads soon, say in 3 months for example? I guess what I'm really asking is if the fluid is in a closed system and does changing pads or rotors contaminate that system in any way that requires it to be changed when this type of brake work is done?