hi all,im new to the jet ski thing.i have recently bought a 1990 waverunner marine jet 650 and i have a few questions that need answering if possible.here goes,when i flush the salt water out the engine there seems to be like black oil coming out the rear of the ski for a few minutes.the thing is, it doesnt have the rainbow effect in the water like oil.can anyone tell me if its oil or not.also having been out for the first time i have managed to put a 4 inch crack in the footwell and i was wanting to know what the hull is made from,it doesnt look as though its made from fibreglass.all help would be much appreciated.thankyou.