I didn't use anything stronger than Windex on the original unit but that didn't work very well. It seems that the plexiglas was softened by the glue and had a tendency to smear when I cleaned it. Since receiving the replacement I haven't used anything more than Windex on it either but since I removed the film immediately on that one I didn't have the smearing problem. I just took another close look and the leathery look is returning to the top surface now and the grey blotchiness on the underside is spreading. I would guess about 80% of it looks gray. I think the grey look is from very small gas bubbles forming underneath causing a delamination. I think this must be a poor grade of plexiglas that it softens so easily. Ultimately, I would like to be able to remove the plexiglas and replace it with a piece of dark glass.