I insure and list all my camera equipment and lenses, including my cell phone on my home owners insurance. My equipment is covered at all times for anything including stupidity if I break or lose something. On a side note I had a non US Nikon D750 that never gave me any problems. On I think the 4th recall I checked the serial number with Nikon. They put in a new shutter and recalibrated focus and updated the firmware at no charge in August 2017. I also have bought stuff advertised as grey market and when I received the item it came with all US papers and warranty (Sigma lens). Its all about the money and Nikon and all others gets paid the same no matter who sells the camera but they got to put on a show for dealers that are required to buy so much inventory. I just bought a new D500 US and a D850 non US. Check out the model number on a D850 sold by BestBuy or Walmart. I think it is listed #1585 same as grey market on some Ebay sites. I think it is a good idea to have insurance no matter the warranty. Just sharing some information and experience. I think if you call and ask if you can get warranty on a grey market item the answer will always be no. I also think warranty is done on a lot of it with no questions asked or any information given other than serial number. I might be wrong with my thinking but I am also going by experience. If it's insured all you need is a receipt showing you purchased.

I did not have the problem you experienced, but did have a somewhat related problem with my new D500 when it quit working with my Nikon flashes. The repair (under warranty) involved replacement of the main circuit board and the hot shoe.

There was no damage to the camera leading to that failure, and Nikon did not document what they felt was the cause. My conclusion is that these cameras are incredibly complex devices/systems built from a large number of highly sophisticated miniaturized components. With so much going on, it is just a statistical possibility that a small number of failures will occur.

The good news is that I have had zero problems since receiving my camera back from the repair center.