Mike,
Your friends helmet does indeed show the first signs of "red rot". Unfortunately there is little he can do to reverse the process. The good news is your friend has caught the issue before it has affected more of the helmet.
The conditions under which "red rot" occur are not entirely known. Treatments are still inconclusive.
The only suggested "fix" for the issue is not really a fix at all but just apparently slows the process down. Curators suggest a change in environment.
Personally I would suggest moving the helmet out of the light and preferably into a airtight container that is in a regulated environment.
Since they are very small spots he could certainly try to use a little Lexol and see if there is a positive effect.
http://www.nationalarchives.gov.uk/preservation/faq/redrot.htm
John
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