Hi my friend has a 2004 Passat. He had it in the dealer for some work and they said he needed new rear brakes and the system should be bled. They quoted him $650.00. We replaced the brake pads and I pumped the brakes to firm everything up. Then we were going to bleed the system and add new fluid. With the engine off I had my foot on the pedal (with really just the weight of my foot with no pumping) and he loosened the bleeder valve and no fluid came out. So we tried the other side thinking something might be wrong with the one and same thing no brake fluid came out. So we decided to forget about bleeding the brakes. When we started the car up the brakes worked fine, but if you stopped and kept your foot on the brake pedal your foot would slowly go to the floor. Like the master cyclinder went bad. We tried bleeding the brakes again with the motor running this time and fluid came out. My question is. Is it possible to damage the master cyclinder by trying to bleed the brakes without the motor running? In the past I have always bled brakes without the motor running.
Thank You

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Mike