So in summary for the B 737 NG:
Fuel leak suspected.
Boeing states most probably comming from engine.
Shut down engine to confirm this is true.
If so thats the end.
If not leak is somewhere else.
Try to get as much fuel as possible out of leaking tank (Airbus)
Enentually restart the engine.
A bit strange at first glance but probability is on your side if you start by shut down.