ok, this could be a combination of things that have occured...
Did you leave your fuel tap on? If you did, and your floats are off, and you have plugged off your overflow, then fuel is just going to run straight into the engine till it fills, so you most likely have your Crankcase and cylinder full of fuel. After trying to start it, fuel would have been pumped into the exhaust by the piston (would explain the leak from the exhaust pipe).
About the Magneto cover leaking fuel?, i wouldn't have a clue as to why this would happen. The Magneto shouldn't have anything in their (fuel or oil). But, this could also be shorting out your bike, stopping it from starting.
hope any of this helps or is relevant.