HP ScanJet 4100C - Cleaning the Inside of the Glass

I have been using an HP ScanJet 4100C with my linux computer for a number of years. I primarily use it to scan old pictures into GIMP for restoration or enhancement. Even though I always kept the outside of the glass clean, I have noticed in the last year that the inside of the glass was developing a cloudy residue. I finally decided to do something about it. Before getting started, I locked the scan head using the sliding green button on the bottom of the scanner. If you open the cover, there are two round rubber inserts near the top of the scanner. Pry these round rubber inserts off with a small screwdriver and remove the exposed screws. This will free the top half of the scanner case. Next, there are two locking tabs about midway on the scanner. These can be released by firmly pressing the bottom half of the scanner case at about the midway point. Once these are released, there are some retaining tabs at the bottom of the scanner case. These can be released by sliding the top half of the scanner case top toward the bottom at which time the top can be removed. I first cleaned the inside of the scanner glass with window cleaner. Then, I used a clean white tissue to do the final cleaning. I put it back together in the reverse order. The glass in now crystal clear! Before using, do not forget to unlock the scan head.