If a motor has been run hot, the piston ring stake pins, the ones that keep the ring from rotating in the land, can come loose. The stake pins are steel and the piston aluminum, the alum hole for the stake pin will open up before the steel pin has time to heat and expand in timely fashion, thus letting the pin come out. Once the pin is out, it will do damage itself, the ring will then work itself around inside its land till a end of ring gets into a port, then its a done deal.
More motors have been run successfully on ethanol than folks want to admit to. You can't let it set up as mentioned, the alcohol will absorb moisture. The worst thing about ethanol is it eats up the older style non-alcohol hoses, seals, etc., then those particulates get into carbs, stops up injectors which will toast a nice motor..