I have NEVER had a problem that could be attributed to ethanol, but I do use the old original Stabil in my small engine gas every time; a double dose when it might stay 6 months or more as it sometimes does in my Mantis tiller. Of course, that Mantis tiller was a reconditioned one and I've only had it about eight and a half years. The Stihl string trimmer is more than ten and a half years old. Those are both 2 stroke. The Toro ZTR with a Kohler engine is a 4 stroke but barely over 5 years old. The only thing I've replaced on it, so far, is the battery.