, to try to answer your question, which is "what do I say to the tech" / "how do I word the problem", I suggest simply telling like it is:
The Kuro is/was advertised as having the "blackest blacks", and your set is showing blacks levels that are less dark than some LCDs you have seen.
(If I understood you correctly)
You say that nobody will agree it's a problem if you phrase it like that. But that's the reality of it. Once the tech is in your home, that's what you will be showing him and telling him anyway. So if someone on the phone say to you that it's not a problem, you're off to a bad start already. You need to find a tech or company that believes in the quality of the Kuro and knows what Kuros are supposed to look like.
I don't recall if you have indicated your location in one of your (many...
) posts? You might want to ask if anyone has recommendations for a reputable service company in your area.
For sake of this discussion, let's assume your set has a problem. You didn't seem sure at the start, but without seeing your set in person or using quantitative measurements, no one can actually tell if it is a problem or not, because we're all using relative terms without a common reference. I suggest you stop talking about the details of what you perceive are the issues, this only sidetracks the discussion, runs around in circle and prevents answers to the real question you want answered, which is where do we suggest you go from here.... I believe I answered that question at the start of this post.
Finally, just as a side note, you say that "just because some people don't know what it could be doesn't mean others also can't or won't". The reality is that the type of issues you're describing could have multiple causes, ranging from user settings in the display, the source components, to hardware failure of different component types. We could go ahead and say, for example, it's the power supply that drives the panel voltages, but what good would that do you? I hope you wouldn't order a replacement board and swap it, because it might be something else and you would waste your money. Of course, if someone could say for sure that problem "XYZ" is caused by failure of component "ABC", then yes, you could go ahead. But the problem YOU are describing is KNOWN to have many possible causes. This is why the experts on the board believe that it will not be possible for anyone to help you without seeing your set.
I hope this helps a little....