Honda BF 130hp. 2001 gas sheen on water
 

I have twin engines. I am noticing a light sheen of gasoline on the surface of the water while idling or flushing one of the engines. I carefully looked around the block of the engine and can see no drips or leaks. While the boat is on the lift, the water being flushed out seems to be where it is coming from.

Any ideas how to isolate this or suggestions?