I’ve put on 140k+ miles on my 340i and still drive it with an E40 custom tune whenever I can manage to fill up. I’ve never heard of any major injectors getting stuck issues other than on some V8s but that’s pump gas even stock cars have it happen. Your tuner is most likely right and it has nothing to do with ethanol let alone his tune. Injectors on these cars are nothing new. They’ve been used for a long time now.