Thanks for all your proposals. I think this MEsuper has a plastic screen. I got the camera yesterday from ebay and examined and cleaned it in the evening. Todays morning I have compared the brightness of the viewfinder against that of my ME, and it is noticeable brighter, so it must be another type. And I have tried already to remove the residue with a mix of pure alcool with water (hat no vodka) - but it seems to be no residue because the damage looks like afore. I downloaded the service manuals from Mark Roberts site. Looks quite complicated to remove the screen. And I wouldn't have a new one to install. So a repair and CLA seems to be the only thing to be done :-(
Have a good sunday (it's getting hot here again) Bernd
