I had an issue with my gas cap not sealing properly when I first got my bike. Sometimes after riding or letting it sit over night you could see where drips ran down the tank. I called the dealer and of course no one ever heard of this being an issue before, but they suggested making sure the cap is completely closed and both hooks click into place. Well, I don't know how you can verify the hooks are in place with the cap closed, but I make a point of pushing down on the cap after filling until I hear it click and then pushing a couple more times and I haven't had any further issues. Even from the start I didn't fill the tank full. Keep in mind the fuel at the station is kept in large tanks underground and is therefore typically cooler and more dense. When you fill up your bike the gas slowly warms and expands and can overflow through the filler neck. Unless I'm going on a long ride, I leave the fuel level roughly 1.5 inches under the filler neck for safety.