As with some Nissan Stealers Andy it is always something they forgot to put back together properly! Not hooking up the angle positioning sensor is wild to say the least and even worse when they turn around and say 'must have already been like this' or 'we have checked everything'!
When you called me asking for the obvious places Nissan should check I felt seriously bad for you! They should have at least 1 Trained Nissan Tech that knows 350z's! I am guessing the reason they didn't charge you much was because you had to tell them what to do and how to fix it. I would write a letter to the senior guy at the dealershit sorry Dealership and to Nissan GB about the service you received here.
I'm glad it got sorted out but Jesus just imagine if they threw an ECU at the original problem!
Rant now over and I am staying off the coffee for the rest of the day.
I'm glad I could help mate and hope you get to use and enjoy the car now