Re the op's lens, I still can't tell even with the larger pic, but I think there's something different happening around the edges to the rest of the lens surface. Most of the surface looks like it's got some kind of film on it, haze from condensation or similar, which can lead to fungus. I have no idea what's happened to the edge.
At the end of the day, unless this is the 50/2 Macro or the 50/1.2, I'm not sure that it matters as the rest of the 50's are not expensive and it's probably cheaper to replace it than to repair it, depending on cleaning/repair costs in your area. It might be worth trying to clean it yourself.