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The original cap on our a1 leaks quite a bit of fuel down the side of the body whenever the jeep is moving and turning. I installed a new gasket but that didn't help. It looks like the cap is not appying enough tension to push the gasket against the top of the filler neck. I bought a new cap from one of the suppliers but it did not fit correctly and was returned. Before returning it I installed both gaskets on the cap and it seemed to seal solidly, but I'm concerned that if the vent in the cap isn't working the two gaskets solution will create a vacumn lock and starve fuel to engine. I did a search of this forum on "gas cap" and "leaking gas cap" but didn't find anything. Any info on how to stop the fuel leak will be appreciated.

If the filler pipe cap locking cams are not worn or bent then a proper cap should seal.

The only solution to your issue is getting a proper cap and checking the fit and function of the locking cams on the filler pipe.

As for venting, your tank has a vent fitting on top at the pickup pipe location. Early M38A1's had a tube connected to the tank vent fitting that ran to the air cleaner and later A1's had only the vent valve there. As long as it remains clear the cap's activity will have no affect on venting.