Master Cylinder or Power Booster?

I dont know if its master cylinder or power booster. Put front and rear pads on the bled the brakes. During bleeding the back brakes didnt seem to have the pressure the front did. But anyway my pedal goes to the floor, before I bled them the pedal went to the floor and got to the point that I rolled out in the lane of traffic. So I bled them (1st time never bled brakes before) and it worked for a minute. Now it goes to the floor but it stays put just way slower to stop the car. I pump them a little while stopping. Master cylinder has fluid and has maintained fluid. However I found a leak that I think is coming from the seal where the master meets the booster. So help I dont know which it is? Thank you Karen