I assume you’re referring to Caddyman’s reply about the smell possibly coming from vapors migrating in through the heater air intake. If my assumption is correct, than you won’t see liquid there. He’s suggesting that the fumes might be coming from somewhere under the hood, like perhaps a leaky injector-body O-ring, and traveling as fumes up out the engine compartment, then being drawn into the cowl vent and pushed by the fan through the heater ductwork and into the cabin.
His suggestion is an excellent one. You might even be able to verify it by putting yuor nose under the hood and having a friend rev the engine while you sniff.