I had a 4.5-14 Buckmasters that I have owned for long while go down a couple of years ago. I called Nikon and got an RA # which went very smoothly and sent it to their repair facility in California.
It took a total of 14 days to get the scope sent in, fixed, and sent back. 10 of those days was transit time with UPS.
I thought they did very well and the scope is still working fine.