I seem to be having problems with my master cylinder. Yesterday when I was stopped at a red light, my car slowly started creeping forward and my pedal was slowly going towards the floor. I had to pump my brakes to stop my car from moving. When I press on the pedal with the engine off, with some constant pressure the pedal will slowly move towards the floor. Does this sound like a problem with my master cylinder? Is this a easy/moderate DIY replacement or do I need to go to a dealership? My car is getting pretty old so I'm not sure if a $3k repair is even worth it at this point. Its a 2005 SR5 w/ 205k miles.