BUP: the dash temp is around 160 at idle and around 140 when running. I already changed plugs, will clean flame arrestor, last time was a couple years ago. I will make your suggestions to mechanic. Thanks

After taking the kids skiing, we went back to the dock and idled for 5-10 minutes and the fuel sheen on lake was approx a 30x30 area. That's when we pulled it out to take to mechanic. It had been running rich since beginning of summer, but never that bad. Seems to be worse at lower speeds.

140 at running is too cold for a stock 496 with a stock ecm cal. That will not help the spark plugs if in fact running 140.

these engine run rich at 140 I would verify temps with the scan tool while running at all rpms.

I was thinking 2008 model but see you said 2005 anyways engine serial will determine what you have especially for ign. coils - the GEN 1 coils can be known to failure here. A scan can tell you if one or any have failed. I already mentioned testing wires and coils on top of.

Just saying because GEN 1 coils if you have them really need to be checked out and produce strong spark.

Has he checked fuel pressure? If it is high check for a delaminating cool fuel module, assuming the motor in question has a cool fuel 3 module.