Yes you can change just the master-cylinder by itself. Pop the hood of your car and take a flashlight and look for the nuts there holding the master-cylinder on the brake booster (14mm?). You can order one from FCPGroton.com, good prices. Bleed it as well as you can before you reattach the lines to it. Most autoparts stores sell small kits that allow you to attach small rubber hoses to the master-cylinder outlets and run the tubes back into the reservoir and then have someone pump the brake pedal while you watch the tubing to get all the air out of the master-cylinder. Takes about two hours to do it and bleed the brakes again. Good luck ....... Mike