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The most common fuel leaks are caused by the drain valve on the Filter Housing Bowl.  However a leak can occur for almost any place or from any o-ring location.
Fix fuel leaks promptly because they cause the fuel to become entrained with air bubbles that can damage the fuel pump and/or the fuel injectors.
Prolonged leaks can damage the electrical harnesses in the engine valley and even cause electrical shorts.  We have seen the connectors on the harness that attaches to the Fuel Filter Bowl turn mushy and short out.  This will blow the fuse and the engine will crank but not start.The harness is about $45.00 from Ford.
Keep your fuel filter changed.  Inspect the bottom of the Fuel Filter Bowl for a mud like substance and use a vacuum extractor to remove.  If this stuff builds up and covers the Fuel Heater Element it will overheat and burn out.  Also if left long enough and if the right conditions exist, it can cause a corrosion effect that will put pin holes in the housing.  A new housing from Ford is about $400.00.
We do not recommend that you remove the plastic stand pipe that is in the center of the filter unless you are replacing the Fuel Filter Element.  Remember that it has LEFT HAND THREADS and it will easily break off.
The hoses that are included in certain NAS kit are Generation 2 hoses.  This hose is rated for Bio-Diesel and Ultra Low Sulfur Diesel in inside and the OUTSIDE. It is very easy to spill fuel when changing the fuel filter and it will run down on to the hoses.  Look closely at the blue factory hoses and you will see that they are cracked and they will eventually leak.  Many brands of hose will have the correct SAE specification number which does not specify outside layer or layer coating.  The Generation 2 hose is expensive and costs more than the o-rings and the stainless bolts combined.  We purchase larger spools to keep costs down.
Also see the FUEL PUMPS Section for additional leak information in the "Fuel pump general info" area.