I noticed some gray spots on my 15-inch Apple LDC display (in the menu bar area) that would not come off with a damp cloth and cleaner. I then remembered a few years ago when I suspected a dead pixel and was advised to massage the spot with my finger. It worked then and worked again today! I massaged the spot for a few seconds and the blemish is history. It is a cheap fix that works sometime. I got lucky today. Dick