If the deal is good, the lens from Japan may not be repairable in the US, but should be repairable in Japan. You would need to ship the lens for repair anyway, it would just take longer to get it to and from Japan. Check with the seller to find out where the lens needs to go for repair if a problem ever occurs. I have never understood why Nikon and other camera makers are so picky about the origin of their product to determine it's repair status. They are all made in China anyway and whether the product originate for sell in the US or another country, it should be repairable anywhere unless it is counterfeit and not made my the company that bears it's name.

MT
I registered the serial number for the lens from Japan 307xxx and from KEH 302xxx and Nikon excepted those numbers in my camera bag on NikonUSA.com. I then removed them and entered a number for 205xxx which I believe (based on the first 2 numbers) is a lens destined for the Asian market and it exepted that also. The drop down window when registering the lens did not have the Model 300mm f2.8 G VR (#2154 with VR in red print) only the #2186 VRII . . So I used that lens model. The Camera bag is the only place I can see for registering a lens.

JR69....You should re read your original message because you really answered your own questions. NUSA will not touch anything not brought in to the US legally (or grey market). In my opinion it is not worth spending your own hard earned money on any lens or camera that have come in to the US (under the table). If and when I purchase pre-owned I ALWAYS ask the buyer where they purchased it originally, a copy of the original receipt and a copy of the warranty (even though it may be expired). If they say it has a Nikon warranty that does not mean it is a NUSA warranty. They may have purchased a generic warranty.

In addition, if you send a lens or camera to Japan for repair, you will have to pay duty fees for the export and import of the lens. I was going to ship an HP Laser printer to Vancouver, BC back in 2004 for a conference that our offices were holding there. I found that it was going to cost more for me to ship the printer to Vancouver from Hartford Ct. than it would to purchase a printer there and turn it over to our Vancouver office. The big cost was the duty fees. And if we had one of our people include it in their baggage, we were still going to have to pay duty fees on it BOTH ways. It was less expensive to buy the HP Laser printer there and leave it for the office. I would imagine that the same would be true of shipping a lens to Japan for repair.
When I worked for Nikon Professional Services (NPS) we had a member that wanted us to supply her with a couple of lenses to take on a photo shoot in Mexico. We discussed the issues with her and found that it was going to cost her almost as much in duties and taxes to take the 2 lenses to Mexico as it would to purchase them. So, we arranged for her to get the lenses from our NPS group in Mexico instead. It was cheaper (less expensive) for all concerned.
My point is that the same will probably hold true on getting a lens repaired out of the USA and shipping it back. Many companies (and I think Nikon is one) will refuse to do this because of the liability and expense.