Leaking gas on side of car..help.

If you zoom in youll see I'm noticing what looks like remnants of gas leaking from the gas tank. I was searching and I've found that mopars didnt use vented gas caps, HOWEVER, the prior owner installed a unvented gas tank (CR11A 1966 DODGE DART GAS TANK,) and a SENDING UNIT -- 5/16", SINGLE LINE. So does that mean if I don't currently have a vented gas cap, it would cause spillage? Or Do I need a vented cap?

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