Originally posted by niceshot getting to the lens element is not a problem but, I THINK it is lens separation. Only way to rule it out is to open it up and clean the lens groups involved. It is in a Bad spot ,meaning it will impact the Image quality, So you have nothing to lose, try cleaning it. Start off using Zippo lighter fluid and finish off with alcohol. Also use Kim wipes. Remember to brush then blow then wipe. A friction wrench should be able to loosen it if not then a Lens Spanner wrench . Good Luck
It's got all the fibers and texture that make me think fungus.
My fear is that taking it apart means I won't be able to get it back together. Using the lens a bit, I've seen some impressively sharp shots around F7-8, which lead me to believe that it doesn't influence image quality too much. My guess is that, at worst, it makes wider aperture shots more glowy.
If I were to attempt cleaning, I would very much like to have a parts diagram, at least. I'm sure the 1.7 lens is similar, but not quite the same.