I have a Nikon 20-35 2.8 here that has clean front element but a decent scratch in the rear element. No idea how it got there as I am always careful with rear lens cap.Also aperture ring is s little stiff. I have looked at the images it makes and I can't see anything wrong with them because of the scratch. Any idea what it is worth? I am clearing out some of my Nikon stuff but no idea if it's worth fixing before I sell it or just flick it off as-is? Thanks!