Hello!
Yes, unfortunately I have already damaged an unit.
I havre tried various cleaning methods, but the surface remains slightly fatted and halos of various kind. The best ways that I have found is use a cotton fiocc moistened with isoprophilic alcohol (the same used in the commercial clening product kits for glasses, lens, tape deck heads, pinch rollers, turntable needle, and so on, but completely pure, without any dye or fragrance), After a delicate cleaning, I wait some seconds, and when the surface is dry, I use another virgin cotton fiocc to removec the halos, with linear movements, from left to right, from up to down ...