Nikon D610: Mirror -ERR-?

At around 77k actuations on my D610, the camera's mirror gets stuck every four shots, and the control panel, LCD monitor, and viewfinder displays the word "ERR" until I click the shutter button and the mirror comes down. This does not seem to affect my shots, but is very annoying.

Does anyone know what's causing this and how to fix it?

Googling, people have done something with using a screwdriver to poke at a mirror pin on the D7000 to unstickify it, but I don't know if this works for the D610 and I don't want to break the mirrorbox.

I also found this YouTube video: https://youtu.be/9tyOa673aaA which illustrates the exact same issue I have, but does not provide a solution.

I cannot send the camera in to Nikon for repairs, as it is grey market and they won't look at it.

Thanks!