The INSIDE of the glass of my Epson 4990 scanner has developed a foggy appearance. How do I open scanner to clean glass>. I've been in camera repair 30+ years and am qualified to do this.

SOURCE: Scanner wont scan transparencies properly

I have the same problem with my 4990. This began when I moved to a new computer running Vista. I've updated all drivers to the latest version including Epson Scan for Vista but the only thing the 4990 "sees" is reflective documents. Negatives are not recognized at all. I know this is probably a different problem from what you are having but the effect is the same.

SOURCE: Film option is ghosted

try to reseat (unplug and replug the TPU cable at the back of scanner, and open epson scan go to professional mode and click on configuration button, go to OTHER tab and press reset all then restart computer and try if film is an option to select.

SOURCE: CanoScan 5000F foggy glass

No problem.
1st step. Remove the lid. It just pulls out at the hinge end by lifting straight up, horizontal if you like. Where the two lid posts insert in the scanner body you will find 2 screws, undo them, no need to remove at this point, too hard. Rememeber you left them in there though.
2nd step. Around the 4 buttons at the control end is a striped trim panel that is the full width of the scanner. Locate the join between this trim and the light grey underside of the scanner body and just left and right of the COPY & EMAIL buttons, Using your fingernails lift with some gentle force. This edge will pop up. Note, the trim panel has 3 location tabs that insert under the grey border edge around the glass. So pop the front edge first and pull towards yourself.
3rd step. Once this trim is removed you will note 4 little grey plugs equally spaced under this area. remove the plugs and you will find 4 screws. Unscrew them, no need to remove, remember point above.
4th step. Time for CAUTION. You will be able to lift the upper part of the scanner up in which the glass is mounted. ***There is a lead with little play connected to the 4 buttons PCB which is attached to the upper panel. To ensure you don't damage it accidently when cleaning the glass you can remove the 2 screws attaching it to the upper panel.
5th step. See if you can wipe it, with a VERY SOFT LINT FREE cloth, without putting you finger on it somewhere......................
6th step. reassembly is the same in reverse

SOURCE: Need a document feeder for 4990 scanner

I don't believe it is possible to add a paper feed to this scanner. The only hopper fed scanner of which I'm aware is the Kodak s1220.
Jeff Underwood 1Scan.co.uk

SOURCE: My Epson Perfection 4990 indicator light is

I had the same problem and first checked the instructions in the Epson manual on the red flashing problem, read the following pdfs: Indicator light or problems

I saw the fluorescent lamp come on for a second before the indicator light started to flash red, so I knew that the lamp was ok and did not need to be replaced. Try this turn off the scanner and try unplugging the transparency lid from the back of the scanner, turn on the scanner and see if the light goes back to green. My issue turned out the be the mechanism inside the transparency lid, I kind of heard an awkward noise when I turned on the scanner, but thought it was coming from the base, I rlocked and unlocked the transportaion lock on both the base and lid, to see if that would fix it but it turned out it was coming from the lid, where there is also moving parts inside using a belt and wheels. On the end wheel closest to the front, the 2 little plastic pegs that hold down the square metal plate with wheel broke off, I could hear them inside when I lightly shook the lid, anyways I opened up the lid by removing the 5 screws and you need a screwdriver to put in each of the little openings around the edge to pry open the lid. I removed the belt and metal plate, watch out there is a spring attached to it, don;t forget how this part works when you put it back on, I found both of the little broken pegs and glued them back on with a strong plastic epoxy glue that I bought at Ace Hardware, I let that dry for 24 hours and then put the metal plate and wheel on then put the belt around the wheel, and now everything works fine.