Hi Peter,
I recently did a vectra with that engine,i had a fault code for one glow plug and advised the customer to do all,nothing surer that one will surely go the next day of completing the job.
After spending a horrible hour or so of what your describing,i finally got ONE fitted.
I put it back together and i dread the thought of having to do another.
A real example of bad e-times.
Good luck and have band-aids to hand for the knuckels.
Dave.