Auto body repair & detailing: spots on canvas hardtop, terry cloth towel, upholstery cleaner

Question
I have a '96 Chrylser LHS with a canvas over metal top that has developed dark spots on the right rear quarter of the roof.  Can't feel any roughness underneath that would indicate any rust so suspect it might be mold or mildew?  Any suggestions before I haul it to the body shop?  Would like to be able to clean it myself if I had an idea of what to use.
Many thanks!  Great forum!

Answer
Canvas can be very difficult to clean because it's so dense.  Dense enough that it is basically waterproof, thus the inability to get a cleaning solution down into it and extract it out.  Best bet is a very mild upholstery cleaner you can get from an auto supply place.  Ask an employee with some experience to recommend something.  As always, try it on an inconspicous area to see the result.  Don't just do spots as it will probably look bad, with cleaner spots being very obvious against the rest of the top.  After trying on a small area to test, do a square foot at a time, using a terry cloth towel to lightly scrub.
Take care.