I bought a new integrated amplifier about a week ago (off topic but it's a Denon PMA-720AE) and I noticed some fogging stains on the top of the black cover. I tried to wipe them out with a wet cleaning cloth but they wouldn't go away.
I think (but I could be totally wrong) that the fogging comes from my headphones as I have left the leatherette cushions on the top of the amplifier a couple of times.
Well, in case anyone else has the same problem, just to advise that the fogging disappeared completely when I wiped the stains with window pane cleaner (I used a paper towel).