Like others have said, you can use a variety of cleansers. Just dont use abrasive cleansers like comet and never ever anything with petroleum distillates or citric based cleansers (AKA delaminane). I use B.E.S.T. Rubber Roof cleaner (buy mine on Amazon) because it claims to add UV protection.
http://epabest.com/products/rubber-r...rotectant.html
Just in case you don't know, you can buy a brush on a stick (AKA deck scrubber) at Lowes and other hardware stores. Much easier to clean that roof standing up instead of on hands and knees
Careful - those rubber roofs get very slippery when wet.
Like Festus said, if you dont know that it's been recaulked recently, I'd carefully scrape the old off and reseal with Dicor. At the very least carefully and thoroughly inspect all caulking. It's a pain to re-caulk but more than worth it.