Check the archives ... here ....
Look/Search for Maine Sail's thread on polishing or buffing. For cleaning gelcoat simply use a caustic based detergent ... a sodium silicate based detergent (Tuff-eNuff), triSodiumPhosphate (TSP), etc. to remove 'air pollution' specks, fungus/mildew (caustics dissolve mildew, etc.) , dissolve/strip old dead wax, etc. .... then rinse and 'bleach' with an oxalic acid mixture. All this can be obtained from a hardware store. Acetone will remove organic 'goos', shoe marks, etc. Then follow Maine Sail's method of polishing and buffing the gel (from the archives, here) ... to restore it to almost 'brand new' condition. archive: http://archives.sailboatowners.com/pviewarch.htm?fno=400&sku=2007012200307.56&id=443490&ptl=#2007012212906.10