Lens mould

In my quest to find a 500mm lens I have found a Sigma 170-500mm f5/6.3 APO lens. It looks in good condition but has a fungus/mould on the inside of the front lens. Can this be cured or is this a definite AVOID at all costs. I wish I knew more!

I wouldn't try opening a long zoom up. However, there are people who can strip and clean lenses. It may be worth asking for a quote from a repairer.

I did manage to clean out a K 28-50mm but that was a bit of a pain, especially when it came to re-setting the infinity position on the focus mechanism.