although acetone, laquer thinner, ether, xylol/xylene, ect will clean grease smudges and oily parts, they are very flammable and evaporate rather quickly.
one of the very strongest grease dissolvers that is not flammable, will remain on the surface and work for awhile before evaporating, and is available on shelves for consumer use is whitewall tire cleaner...
it is what wrecking yards use to spray on greasy parts that they take off to loosen and dissolve years old build up (they buy it in 55gal drums)... its very effective if you have 10 minutes for it to work before spraying with water...
BUT... stained gelcoat may be permanent even after getting any oil residue out of it....
sometimes the stain is caused by an organic compound that can only be removed or bleached with a strong acid... most greases have organic compounds in them to thicken them..
so i would try soaking the stain with a rag wetted with whitewall cleaner for an hour or two, followed by a rinse... then a 30 minute soak with muratic acid (I use hydroflouric acid) in the same manner... if that doesnt remove it, it cant be removed removed without taking the gelcoat with it.
