Re: Gas Caps
You can add an 'O' ring under the cap's rubber seal. That will stop the seeping usually. However, there is an opening where the cap vents to the atmosphere that can seep due to vibration, especially with a full tank.
Look at your fuel cap and you'll see a dented in spot, a peen, on the outer edge. It is there to distort the inner and outer cap parts and causes a small separation where air can get in but sometime it also lets fuel out.
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