I recently had some ERR messages on my D500 that I was pretty sure were due to communication problems between the lens and body. Time to clean the contacts. I used alcohol and a lint free cloth, didn't seem to get much crud off the contacts and mounting ring, and the problem persisted the next time out. So this time I went into the basement and grabbed my can of Deoxit, sprayed a little on a lint free cloth, and tons of black oxidation came off of the contacts and on to the cloth. Not a single ERR message since. So, I'm just saying that if you really want to clean your contacts well, I think Deoxit is worth the $15 or so for a can. You can get it through any electrical supply or hardware store. This stuff is also great for cleaning up volume and tone controls on electric guitars (or basses in my case), amplifiers, or any similar application.
