I have a non grey market 300mm f4. When it was just out of warranty the AF-S motor began to screech on focusing. Fixation, the accredited UK repairers told me it was quite a common problem with this lens. Nikon wouldn't repair it although the warranty was only a month out of date and it cost me £350 (US$525).
If you buy a grey import and something happens you will have no warranty at all even in year one. I learned the salutory lesson of Caviat Emptor or Buyer beware.