A leak doesn't always mean fuel coming out but maybe in your case air getting in displacing the fuel allowing it to drain back. I would lean towards fuel filter leak at lines or the shrader valve.

 

The check valve in the fuel filter may be shot, but it should still hold fuel up there unless there is an air leak into the fuel system.

You could block off the fuel return line from the fuel filter and see if that helps the start problem.

 

PLC7.3 stated that there was a check valve in the return line. Since the return line would only go into the top of the tank and not under the fluid level, if it were bad wouldn't it allow that line to pull air out of the top of the tank above the fluid level and therefore allow the entire line to drain back to the tank? If it's been driven recently it starts right up, it's only after it sits overnight that it takes a lot of cranking.

 

I started experiencing a problem starting with my 6.9L also, but not in the morning. In the morning she fires up on the first crank. BUT when she is warmed up and I stop somewhere for more than 30 mins or so then she wont start... well VERY hard to start.. let her sit 4 hours and she fires up on the first rotation. Apparently she is not getting fuel.

When I spoke with a diesel mechanic at ford he said it could be due to the ULS fuel and suggested adding a lubricant to my fuel. His theory is that my older IP cant build pressure when the fuel is heated. Is this something others have experienced? Or could this also be related to the fuel lines.. a restriction or air leak or something else?

Anyone know if the ULS fuel is also causing leaks? When you purchase a new set of o-rings will it be made with the new materials? Or is that something you have to special order?