I've had two lenses that bit the dust through fungus growth (living in Indonesia) and they didn't look like that. Much more of a mottled effect.  Is it possible that sand has got in? Scratches from grains of sand? But I don't they should have a major impact on the use of the LSD.(I've got one too)  Pity from a cosmetic viewpoint of course, but the LSD only shapes the light and I would not have thought scratches like that would make much difference?