Through the years I've gotten away from ethanol for mowers and 2 stroke tools....anything that may sit for extended periods. Some of the stations sell 100% gas for a premium. Others I know use additives to overcome ethanol use. I've had the fuel and return lines deteriorate thru time to the extent the intank filter came loose from the line. A severe crack or break is pretty evident...a smaller one could cause the intermittent problems you describe.