The arrangement of brake system components that use fluid to transfer controlling pressure to the caliper is called the brake hydraulics. Without this transfer, your Cadillac XLR would be unable to reduce its speed or stop. These actions are important to both your safety on the road and that of other drivers.
A failing brake system is an accident waiting to happen, and you should never ignore early warning signs of malfunction. This might include the feeling of a spongy pedal (that is, the brake pedal compression is soft). Replacing parts immediately can prevent further Cadillac XLR damage. Keep your fluid levels high to avoid a problem, and bleed all air from the lines.