Brake pedal slowly goes down at red lights?

Common reason why the brake pedal slowly drops with your foot on the brake: Master cylinder seal failure. When you push on the brake pedal, brake fluid is sent from the master cylinder to the wheels. If the master cylinder seals are failing, they can be bypassing this hydraulic pressure, allowing it to escape into the reservoir (and ultimately back to the master cylinder again), and eventually cause a sponge feeling.