Yes, what Zeiss says is true. You must be extremely careful with preventing fungus. Once fungus visually appears on one lens, it is almost certain that one or more lenses that have been stored and/or handled with that contaminated lens has fungus as well. You may not see it in the other lenses at first, but the spores are probably too small and still incubating. (This is one of the reasons why I do not purchase used lenses from Asia, which due to the extreme humidity (Hong Kong, Singapore, Thailand, etc.) have a much higher probability of fungus infection.)
Unfortunately, your 85/1.2 should be destroyed. Otherwise, you risk losing all of your other lenses as well. I would not trust anyone who says that they can clean it, unless they work for a disease control center and have access to bio-containment equipment (extremely expensive). However, if you really want to try and save this lens, you will have to purchase all the tools to open and clean the lens yourself, work in a location that is isolated, wear disposable lab clothing/masks/gloves/etc., open and clean the lens thoroughly (using the right chemicals to kill fungus, yet not deteriorate/damage the lens surface), then dispose of everything (tools and clothing) and finally irradiate the lens with UV light.
To try and save your other lenses, you can try to irradiate them with UV l&s to kill any incubating spores. Then, keep radiating them regulary especially after each use. When not in use, you should store your lenses in an electronic cabinet that removes all moisture and maintains constant humidity. These cabinets are easily found in Hong Kong and Singapore.