Mildew stains on tubes

[Explorer94]

I recently purchased an old Sea doo explorer in need of TLC. She is cleaning up well but the tubes have small black mildew stains on them. I have used a number of cleaners to try to eliminate these stains but to no avail. Any ideas would be appreciated. The tubes are very clean at this point, just these stains remain(I think there mildew). Thanks in advance!

[bicyclejuju1]

I used a non abrasive bathroom cleaner with bleach on an old 2001 Avon i just bought and it worked wonders. The hypalon seemed to hold up to it. Afterwards I applied a good protectant. Not sure if it was the correct thing to clean w so I'd do a test area first.