Only had my Z since February but E10 high octane works fine in mine. It’s all we can get around here so the PO must have been using it for years. I think it doesn’t age well, so don’t fill up before putting it away for the winter, or add some kind of fuel stabilizer. It can gum up carbs and deteriorate old rubber hoses too, so I hear. I run it in my 85 Jeep Cj7 with a carb for years and have no problems. Best way to prevent problems is to DRIVE it! 
