I spend one day each week browsing around in the used camera shops here in Japan; there are dozens of these shops, and they sell pretty much anything and everything.
Besides OM gear, I also shoot Nikon, Leica, Canon, Mamiya, Yashica, and large format. I am always on the hunt for curious items or good deals. I've looked at hundreds of cameras this year, and perhaps thousands of lenses, and I'll be the first to tell you that fungus is not at all common on Zuiko glass. In hundreds of examples, I've found only 2 Zuiko lenses with visible fungus, and one of these lenses was mounted to an old OM1 which was literally corroded into a greenish color.
I can't count how many Canon lenses I have come across with fungus in them. It is nearly universally present in the FD lenses which I find in the "bargain" bins. It's less common in Nikon glass, but it's still more common in Nikon lenses than in Zuikos. It's a shame that Canon lenses get so much fungus, my Canon collection is larger than my OM collection, and I love to use my old F1.
Fungus is also a problem in Rodenstock lenses, 3 of the last 5 used lenses which I have looked at had fungus present in them.
Fungus is not a common issue in Olympus Zuiko lenses.
