Age of the units? How much service? Valves adjusted at about 150 hours?
The ethanol question is a good one. I had to replace a carb on a Stihl chain saw because the ethanol destroyed a seal. I'm unsure why the ethanol has not done damage to my other Stihl products. The chain saw gets little use, but the other Stihl handheld units (four of them) get constant use.