... after thinking about it,... Your problem with gas cap leaking probably caused this... but, simply sealing the cap rim won't fix it...
The reason caps leak, is that the tank is overfilled...
Sealing the rim, allows you to overfill without leaking, but the gas is still up there,.. that gas, is working it's way into the cap leaving a residue that lacquers up and clogs the vent...
Best to try to fill a little less,... and this problem won't recur...

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I'd use whatever cheapest,... "cause I'm cheap...

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