The replacement part for your Cadillac brake master cylinder can be a new or a rebuilt part. It is the seals on the piston at the bottom of this component that tend to fail requiring it to be replaced. This is the component of your braking system that compresses the hydraulic fluid which then exerts the force against the pistons in the calibers and wheel cylinders to apply the pads and shoes against the rotors and drums that stop your vehicle. To help prevent the necessity of replacing the brake master cylinder on your Cadillac, the replacing of the brake fluid should be done periodically, as well as when a component of your braking system is swapped out. This will remove any of the moisture that might have accumulated in the system which could damage it. The failure of a Cadillac brake master cylinder cannot always be noticed by looking at it for an external leak. Indications the brake master cylinder is failing are usually the same as a leaky brake hose or line; where the brake pedal feels soft. The brake pedal can also continue move towards the floor when pressure is being applied but no additional stopping force is experienced by the driver of your Cadillac. The parts that usually fail on a brake master cylinder are the seals and the piston. A rip or tear will allow hydraulic fluid to seep past them which reduces the amount of pressure being applied to the brake system. In time your Cadillac will experience total brake failure if this is ignored. If your brake pedal is travelling a farther distance than it had previously, take you car to a shop and have the technician inspect the brake master cylinder and also look for leaks so you can be safe while riding down the road.