Freelander 1 TD4 injector leak?

I have a mystery diesel leak (small quantities but annoying since I can't find it). It is not the spill rail and does not appear to be any of the high pressure connectors. While looking for it today I noticed that injector 1 is sitting about 1mm higher than any of the others - I am now out of my comfort zone when it comes to knowledge of diesel engines but it don't seem to be right.

A ruler laid across the connectors confirmed that injector 1 is higher and looking at the mounting stud, there is a gap between the underside of the collar and the nut which is locking the stud. Injector 1 also has fewer threads showing above the top nut so I am pretty sure it is not in right - could this be causing my leak?

I am going to have to take the inlet manifold off to be sure but the nuts above the collar do not seem to want to tighten down any more. I assume that I am going to have to get the injector out, clean up the hole and the injector body and put it all together again.

Any other thoughts?

Make sure the collar is the right way up, or someone may have even fitted an injector leaving the old copper washer in adding another to the injector when it was fitted, all guess work I am afraid.