Originally Posted by JonL

That knocking noise... did you check your oil level? Did you have oil pressure on the gauge at idle? Don't drive the car like that--not even a little.

As far as the rear seal leaking... if you can see the front side of the flywheel (the side away from the transmission) look for a characteristic pattern of rays coming from the center of the flywheel. This would indicated oil leaking from the main seal onto the flywheel and being flung outwards by centrifugal force. If that front surface of the flywheel has no evidence of oil like this, the leak is likely elsewhere.