Dan, I just looked at mine: it's a little dark even with the garage light on to see the spots, but I noticed the window has an area along the bottom were water (etc) can come in contact with the under side of the glass. Could this delema possibly be caused by calcium deposits were the water sits at the bottom underside corners when drying due to gravity/ roll off? If so, a q-tip and a little viniger should do the trick.