I'd say old man time is to blame for that mess..10% ethanol fuel, not so much!!
I agree with 'tri again' on the clean up, best to just clean and keep it full to keep the moisture and air back at it..
Drain, dry and marine fogging oil spray the inside during periods of storage.
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)