I have asked for help on this before and never received any advice. Apparently it is a very tough problem. It is really painful to have to keep cleaning up old saddles and know they are deteriorating. In my opinion, mild bleach solutions do not work. I have never tried vinegar, but these people don't think much of that either.
This article is helpful and I'm going to try the product and give back a report.
http://www.leathertherapy.com/
Right now New Jersey is a perfect fungus testing ground.
Joe Bender-Zanoni
Great Notch, NJ