This is on the '70 GTO. The brakes have not been working and the pedal goes straight to the floor. I noticed there was no fluid in the rear of the MC so i added some (ignoring the question of why there was none), bled the brakes and the pedal seemed a bit harder, but weaker as we went. So we started it up and gave the brakes a shot, but there was no brakes.

Then I noticed leaking brake fluid from b/w the MC and booster and I assume that is the cause of air immediately getting into the system and causing there to be no brakes.

So what could be the cause of this leak or will I have to take it apart to see? Thanks