I found a 150mm Omega enlarging lens that was suffering from some fungal problem , I just cleaned it up with some iso wipes and it it now as good as new and is my main 4x5 enlarging lens.
I have seen some lenses that are totally trashed from fungus with pitting that I could even measure.
B+W are amongst the best filters so it is worth saving. if it is just a UV then I don't think it will have sheets where any thing can get in and as far as I know the only filters that do have sheets are the polarizing filters where as the Kessaman range of B+W filters use a special edge seal so this can not happen
I've seen lenses like that too (pitted and etched). Those lenses are not salvageable. It does happen, but often it is just that the guy trying to clean it was not using the right stuff and didn't get it all off. In fact, once that stuff has been on there long enough to build up some of the crud it cements itself to the glass with, conventional cleaners can't touch it (it's waterproof). The hydrogen peroxide and ammonia mix will dissolve it though. About half the time, and only if it has not eaten into the glass yet, the lens is salvageable to the point that it will be like new. The other half of the time, it really is ruined -- but you don't have anything to lose at that point and you can't always tell if it is etched by looking at it.
I tried cleaning with soapy water but that didn't shift it and I got worried. I followed Fallis' advice to use that 50/50 mix and it sorted it out perfectly, especially after he said that soap wouldn't shift it.
I'd rather not use UVs but they've saved my cack-handed bacon before so have to buy good quality ones, at £50+ a pop for a sheet of treated glass I'd rather make an effort to recover it than chuck it away.
It is possible, but before doing anything drastic, try this: Go to the drug store and get some hydrogen peroxide, then go to the grocery store and buy a bottle of ammonia. Buy some cotton swabs too. Work up a small amount of a 50/50 mix of the ammonia and hydrogen peroxide. Dip the swabs in it and scrub at the white dots with that. Soap and water will not remove the fillaments of most types of lens fungus, but this will; it dissolves them.
There were several guys sending me old lenses for a while that they had bought for next to nothing on ebay, because they were "ruined" by lens fungus. I was making a profit cleaning them up and sending them back looking and working like new, until I made the mistake of telling them what I was doing to them. Once they found out how easy it was, they didn't need me anymore.
See, once the stuff has been killed, it still has to be removed. It dries semi-clear and half the guys out there who think they have waited too long and the fungus has etched their lenses actually just have dead fungus filliments stuck to the glass. The stuff cements itself to the glass and it will not come off with soap and water, alcohol, vinegar, sunlight or any but three of the so-called "cures" for fungus out there. Bleach will work, but it can cause problems with dissolving stuff other than fungus (and, of course, with bleaching). Some other "cures" I've heard of would etch things worse than the fungus. Cold cream has something in it that will dissolve fungus, but it is greasy and it is a lot harder to clean up after the fungus is gone. The hydrogen peroxide/ammonia mix works and is a lot neater. It even dries up without leaving a residue. One word of caution though: don't use it on a soft coated lens unless you have dilluted it to about 5%; it can loosen the coating.
Oddly enough, the only other thing I know of that will melt away lens fungus is cold cream. Of course then you have the huge problem of getting all the cold cream off. Lots of stuff kills it, but there is not a lot of stuff that will remove it.