There are three main metal fuel lines on the driver’s side of the DT466E engine. If you have tried to tighten these lines and there is still fuel coming from the fittings, then it is time to change the o-rings. The first line goes from the fuel filter manifold up to the back side of the fuel pump. The second line then leaves the front of the fuel pump and heads back towards the fuel filter manifold. The third line leaves the fuel filter manifold and heads up to the fuel rail which feeds each injector the necessary fuel.
Due to these o-rings being soaked in diesel fuel all the time, they do not last forever.
Remove the leaking fuel line and inspect the end of the line where the nut is. If you look down inside you will see some rubber, but it will not look anything like the new o-ring. You will need to take a small pick tool and dig out the old o-ring. Usually these old o-rings do not come out easily. Just keep digging and picking at it until you have every last piece of the old o-ring removed. Once you have it clean, then the new o-ring can be placed inside and the line reinstalled to its proper place. Chances are if one of these three lines were leaking then the others might start leaking some time soon. If you have the time, it wouldn’t be a bad idea to change all six of these o-rings (two on each metal line) while you are working on the one that was leaking.
Below are some picture illustrations of what the lines, old o-rings, and new o-rings look like.