So a few days ago just as I was parking my 2000 Corolla in my yard, my brake pedal dropped to the floor. I didn't see any fluid leaks nor did the brake warning light come on. With the help of my dad I checked the brake system earlier today. No visible fluid leaks anywhere. We tried bleeding each brake and it seemed like there was very little fluid flow to the rear. No lines are leaking and nothing I can see is broken, so I was thinking maybe the master cylinder has gone bad. Is that possible? The car has 447210 kms on it.