nice work bigmac... That is exactly my filler assembly. That cap is different than mine however. And while I have a segment of broken chain on my cap, and also a segment of broken chain on my boat, I believe someone along the way may have dropped my cap and replaced it with one with identical size and threads, but no venting mechanism... Seems like if they rely on than cap to allow air in, and if it does so through the tool holes used to remove the cap, that water would easily collect in the holes and be sucked in the fuel system as air was drawn in to replace fuel..
To those that have responded that they get a sound when popping the cap, do you still have the original cap on the boat as far as you know?
Big mac, all the research I've done seems to agree with what you've stated about fuel systems being required to vent to the atmosphere. But I cannot find a provision on my boat for this to happen if it isn't in the cap itself...