I drilled a hole in the top center of both my caps. What was happening on my bike was the fuel would slosh and the engine would warm it and it would pressurize the tank a little, then when the fuel splashed up near the filler neck, it was forced out around the crappy gasket.

I haven't had any problems since I drilled them.

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If it ain't broke, and you mess with it long enough, it will be.