Be vary wary of what they say. I have a neighbor who is a mechanic and last year we purchased a new car that died while driving a week after we bought it. It had a vacuum leak. They accused me before they found the leak of putting in E85 and told me it wouldn't be covered under the warranty if that is what I did. I was telling my neighbor(the mechanic) and he said even if I had put in E85, which I didn't it wouldn't really do anything to my car. I found this on another site for you.
FACT: One tank won’t hurt. Some dealers are spreading rumors and charging $300-$3000 for one tank of accidental E85 use. E85 use in a standard vehicle may cause misfiring and a rough ride. Your check engine light will come on. One of our customers reported that they tried E85 in their new Cadillac. The car ran so poorly that they got half a block. They had it towed to the dealer. They were changed $2000 to have the fuel system purged, new fuel injectors installed and a complete fuel management system replacement. The dealer also voided their warranty. I recommended that they report this dealership to the attorney general of their state and the BBB. This is robbery. I have people call me all the time and ask what they should do in this situation. I joke and say, buy an E85 conversion kit! If you should accidentally or on purpose put E85 in your vehicle, drain the tank, put in regular gas and all will be well. Folks in the Denver area are so grateful when I help them, they offer me the E85 for free. If you use E85 ethanol without a conversion kit or in non-FlexFuel capable vehicles for extended periods, you really can ruin your engine. One tank: don’t worry.