" I suspect that the gas absorbs moisture (water) from the air over time and that ethanol/water mix is then insoluble in the gas so it settles to the bottom."
Jeff, I think that is true - I am not sure of the chemistry, but if you open an old float bowl, you can see the separation, unless it has already turned into a gel!
1. it can attack fuel lines
So the synthetic fuel lines aren't ethanol resistant?
While it is not logical - I have seen the damage - typically "tygon" style tubing seems to breakdown and needs to be replaced.
2. it can attack aluminum (corroding)
Aluminum where? The fuel tank or combustion chamber?
The fuel bowl and the carburetor itself - specifically the ports, when they are corroded, it is a "throw it away and buy a new carb" day!
3. if can create a "gummy"mass in the fuel bowl or filters and when that gets in the jet it requires a carburator job.
I've seen that in my weed eater and leaf blower requiring a new carburetor but not in my lawnmowers or chainsaw. The generator has had some gummy varnish in the float bowl that caused the float to stick. Easily cleaned by removing the bowl and using some carb cleaner.
You might have caught that soon enough - I would suggest getting a "mechanic in a bottle" (FOLLOW THE INSTRUCTIONS!!! or look on You Tube - get ALL the gas out, get the MIB into the carb however you can) to get a "deeper" cleaning of the fuel paths to eliminate future problems. Because if the float was stuck, then the next step is that crap is going to get into the jet and again it is "New Carburetor day!" THE last thing you want is a problem with the generator when you need it...