It may just need the lenses wiped off, or what happens sometimes is that the glue that holds the layers of glass together to form a lens goes bad. One is a relatively easy fix. If the glue is bad, it's not repairable.
You didn't say which sight you have. There are two different styles. One has the lens that you look into at the top, the other is at the bottom. I have the latter, and had to take it apart to fix it. I wiped the lenses clean when I did that, and they're fine now. Unscrewing things without damaging anything is the trick.