If the previous owner used bad fuel, it could have caused the fuel lines to turn to goo, yes. What's really frustrating, and I've had it happen to me plenty of times, is that you clean & kit a carb, only to have gunk from the tank and/or a piece of fuel line goop clog the carb again. Cleaning the tank (especially if it's metal) and replacing the fuel lines is good insurance, and with practice doesn't take too long.
It's been my experience that the most frustrating part of replacing fuel lines is not knowing what size to use. I tired of taking random parts to my local O P E parts desk to find the correct size line. So one time I said, "how many sizes of fuel line do you guys have?" His answer was, "6, but we use these four sizes the most." I asked him to give me 5 feet of the main four and 2 feet of the other two. Easy to store in a plastic container and I know that 98% of the time, I have whatever fuel line I need.
To answer your question, I use E-Free because it's 15 minutes away from my house. I also treat my cans with regular Stabil and a splash of over-the-counter fuel injection cleaner. Whatever's on sale at the parts house. I honestly can't vouch for whether or not they make a difference, but it's cheap insurance in my mind.
As for the Stabil "de-ethanoling" stuff, I'm skeptical. But to be fair, I haven't done any sort of experiments or anything.
