I think I've an air leak! 300tdi

Hi All
So, when the fuel tank is half empty or less and the vehicle has stood around for a few days, starting can be troublesome.
If the engine doesn't start immediately, it takes a lot of turning to fire it into life.
I'm think there's an air leak in the fuel line, which is causing fuel to run back into the tank.Alternatively the fuel lift pump NRV is faulty.
The previous owner had replaced the lift pump, presumably with this in mind, and a few years ago the fuel tank was changed.
I cant see fuel leaking out of the lines, but i suppose a very small leak could allow air in but not fuel out.
Is there a proprietary NRV that i can install into the fuel line, or should I be looking elsewhere to solve the problem?
Thanks in advance for any help.

The injector leak-off pipes corrode, degrade and crack as they get old ... These are the samml, maybe 4-5" pipes that run from injector to injector and to the injector pump and are usuallt cloth covered ... Get a length from any motor factors, easy fix.

'course there are other possibilities too ...

As above - check all the connections, it's easy to get them mis-aglined, especially at the lift pump. Look for marks on the olives to check. A few people have used clear tubing to see where fuel is getting into the system with success. Cheap lift pumps frequently don't last long.

Thanks guys.
If the air is getting in on the return side, providing the lift pump NRV is working should this cause a problem?
I've seen those spill pipes. They're made of a cloth material and just pushed on. Should they be clipped on?

Is your battery getting low after a few days and not turning it over fast enough to start.
Try the same circumstances with a fully charged battery and see if it starts first kick.

Could be, but it turns over quite fast. Even after a few days it always briefly fires, but unless it catches straight away it takes a lot of cranking.
When the tank is full it always starts first kick.

The problem is most likely on the inlet side. I have a section of clear pipe just before the lift pump on mine and can check for air getting in. A possible problem with yours given it starts when the tank is full is a pin hole half way up the pickup pipe.