Are you saying that it won't start, but once it does it will run all day?

If so then I'd be checking for fuel leaking back on the injectors or drawing in air on the filter head or fuel pipes. It doesn't need glow plugs to start unless it' sub zero temperatures so even if they are not working it wouldn't have any effect on it actually firing up.

Have you checked compressions? They are a pretty much bomb proof engine but still can have the odd issue here and there.

If it rolled into my workshop first thing I'd do is pull off all the leak off pipes and electrical connections, crank it over and do a leak back test. Any fuel coming out of the leak off ports on the injectors with the electrical connections off and the injector is fucked.

Then if that test shows nothing, I'd have it on a separate fuel supply from a jerry can direct to the back of the pump and see how that goes. If it cures the problem, time to have all the fuel pipes and filter head off for vacuum tests and see if there is any leaks where it may be drawing in air.