My 99,2500 auto (96k miles on the truck),has a fuel leak coming, from I believe, from the return line above the starter. The nut on the return line was not quite tight, where it 'T's off. I tightened it but still it drips.
Funny thing is that it only leaks when I am pulling our 10,000lbs trailer. Doesn't leak when not pulling a load.
It drips just enough to undercoat the truck and get the back bumper misted on a 500 mile trip.

Is there 'o' rings in those fittings that need replacing?