1999 Jackaroo fuel system.

I'm hoping somebody may know more about this than the Holden agents. Referring to the common rail system of the turbo diesel Jack, we found that the modification to the injectors supplied by Holden consisting of a steel sleeve and O ring was faulty. The O ring was too "fat" and as soon as the injector was tightened down the O ring was ruptured leading to fuel leaks and difficult starting. This has now been rectified with "thinner" O rings which seems to have solved that problem. But what I would like to know is how this leaking O ring allows fuel into the cylinder? The copper seals were fine, and I would have thought that when the engine was switched off the injectors would be firmly closed either electrically or by a spring? Am I wrong? Peering down the injector hole I can't for the life of me work out which is the common rail port and I am reluctant to dismantle an injector just to have a look. If anyone can explain this to me or better still come up with a diagram of the injectors and ports in the cylinder head I would be eternally grateful. Previously after leaving it over night it would refuse to start until I gave the priming pump a few pumps, it was always slack. Now the priming pump stays firm and it starts with no problems. Sorry to be so long winded about this but it is something that has puzzled me for some years. cheers to all