Hi hope that your repair will be fine. I don't have any fast zoom, therefore I have no experience with these issues.
I completely understand that gear can't be perfect and that there are some tolerances under which we can't ask Nikon to go. But, they should make these tolerances public. For instance, they could state:
- We can't tune a camera so that there is less than the following AF Fine Tune units of difference in between the AF sensors: - 20 for a f1.4 glass - 15 for a f1.8 glass - 10 for a f2.8 glass - Etc...
That's what a serious company would do: give their clients their error bar so they could know what to expect, and fix it in repair centers when the product is not within the limits.
I have heard that Zeiss test their lenses before being shipped. They measure the MTF curve of the lens and if it is not within a specific range, the lens is disassembled and built again.