The original one I had wasn't just a simple O ring, it was thicker and the hole was shaped in such a way as to easily allow fuel to flow properly on reserve. In trying to fix mine I inadvertently plugged up the reserve hole which had I not found out at home could have caused a real headache.
That being said, I'm pretty sure I just bought a pack of O rings and found one which fit well enough. No problems since. At least not fuel related ones.
