Prior to doing any of this I had called Apple to see what kinds of cleaners I could use on my iMac. I used the rubbing alcohol straight out of the bottle onto the paper towel - did not dilute it. My iMac had a very visible film of rubbing alcohol residue all over it after I finished wiping it down with the rubbing alcohol, which I cleaned up with a dry cloth. The paper towel wasn't wet enough to drip, but very close to it. It took 3-4 tries with a paper towel soaked in the rubbing alcohol to get it squeaky clean again (I have a skin condition that requires me to put lotion on my hands/forearms and over time the lotion managed to get all over the screen and around the edges of the iMac from moving it around).
So I cleaned the outside of my Late 2013 21.5' iMac with rubbing alcohol (70% isopropyl alcohol), including the screen and around the edges of the screen.
