FWIW - I just damaged the front element of my 90mm Elmarit-M. At least I'll take the blame for it but I have no idea what happened. I noticed something on the front element, tried microfiber cloth and light moisture (breath fog) with no effect, then tried an alcohol swab. Whatever was on the lens the combination of that and the alcohol swab took the coating right off. I still have no idea how whatever it was got on there as I've always had an IRCut filter on the lens. Fortunately the lens still seems to perform well, at least it has in the limited testing I've done so far. I suspect I'll notice the lack of coating when a really, really nice photo is spoiled... <sigh>
Bruce
Bruce