I have just inadvertently tested the storage life of D-76 stock solution. I normally make up 1 gallon of undiluted solution using distilled water, put it up in 1 liter heavy plastic bottles with as much air as possible squeezed off. These I then dilute 1 to 1 as needed. Yesterday it seemed time to mix up a fresh gallon. Searching around in my storage cupboard I found to my chagrin a liter bottle, unused, labelled 3/24/2010. It had been kept a room temperature, and in the dark. Since I had a cassette of film used just for fooling around I processed it, the results look good. Kodak, with commendable caution, cites a 6 month storage life. While I can't recommend over two years, at least it does seem to work properly.