Did the tech recommend any particular type of additive for fuel. I tend to put some stabil in my tank every couple of fill ups and always at the end of the year. I don't know if Stabil has any "anti-water" capabilities though.
This is a good link to explain water attraction to Ethanol https://www.youtube.com/watch?v=xzFzYoxxA10. I did some research after finding 4 gallons + in my tank of 125 gal. but it might as well have been all water as it was past the pick up tube. I used Seafoam but not Ethanol treatment. I see not that Seafoam makes an Ethanol treatment which leads me to believe the original does not combat Ethanol efficiently enough. I have a carb'd motor and at about 2000 RPM to boat died luckily with no bad damage but sounds like it could have been really bad. I had must of used what was in my carb and water separator and made it about a half mile the first trip of the year (2012.) I probably put it away with a couple and picked up more over storage as it sits in the water. You are probably right on about the gas station. If you used 89 oct or 93 it may be sitting all winter collecting water while cars use 87 and come boat season we get it. They are supposed to have water separators at the station too but you know how that goes. Maybe a call over the weekend to the station when kids are working (and less likely to cover up) they may admit to hearing issues or if it is not near a marina you may be able to go back and it is still in there for proof. A boat repair shop local to that gas station may have info as well.
Great video, great songs, no bad hats. I would love to make a trip there myself. Sorry to hear about the motor