I purchased a used 85-300mm lens online a few days ago. It works fine, with no problems at all (I think), however, I noticed this morning that there is something inside the lens, right between the number 7 and the MC.
I'm not sure if it's fungus, it looks to be some kind of moisture, and it doesn't show up when I look through the viewfinder. However, I'm concerned that this will eventually affect the lens' performance, and eventually spread until the lens is unusable. I really don't want to return it, is there anything I can do about this?