Anyone interested in some type of rubber eyecup needs to make sure they find one that will fit a specific bdy. For example, the eyepiece of the D500 is different than the D750. I believe most, if not all, eyecups are third party. So 06Honda should be able to find one that will specifically fit the desired body.
I still have my N90s as well as my N70. At some point, I replaced the original eyepiece of my N90s with a Nikon one suitable for my eye prescription (now Nikon has built in diopters). Unfortunately even though I screwed it on tight, it fell off - at least I found it when I retraced my steps later the same day. So be sure to also read reviews on how well an eyecup will stay in place.