Have just completed my 6 monthly sweat in the box, strangely enough our current sim. detail includes a fuel leak drill. (It was set up 3 months ago, so someone in the Training Dept must have a crystal ball - wonder if it can forecast the stock market??
)
Anyway, back to the question - A340 drills basically say "if you are SURE it's from an engine,(because you see it leaking through the window) then shut the engine down; but if you don't know where it's leaking, then close all the crossfeeds." This seems fairly sensible to me - it should minimise the potential loss of fuel until you can sort it out or get to a runway.
The drill then goes on to say, descend to the gravity feed altitude and switch the fuel pumps off because this will minimise the potential loss of fuel - if an engine subsequently flames out while there's still fuel in it's tank it's probably because the leak is in that engine, or it's feed line - (fuel pressure without the pumps being insufficient to service the engine and the leak simultaneously.) Once you've secured the engine you've probably solved the problem.
This all seems to make sense to me, any comments?