I've had my Z since new and now has 177,000 miles on it. It has long stop being my daily driver (I only put 700 miles on it per year) but I keep it pristine and want to keep it that way. I guess there is not enough factual info out there yet to determine the fate of older model high performance engines using E15 fuel (that's fuel with a 15% ethanol blend). I know that one should "not" use this type of fuel in lawn mowers, chain saws, edge trimmers, etc. Hopefully definitive info will surface soon about older car engines.
If it's broke, try to fix it...what's the worst that could happen...IT'S ALREADY BROKEN!