Sorry to hear about the problems with the vent & cap... based on reviews I read before buying it and the posts on here it sounds like your situation is not the norm, these vents work good 99% of the time & I like the roll over feature for a little added security.
As for the vented caps, very strange you had so much trouble, i use a basic gates repro vented cap bought from rock auto 10+ years ago, same cap sold at auto parts stores, it vents exactly as it should, its a 1 way valve that only allows air in, not out, can verify that by sucking on the back side of the valve, takes a little force but you can tell when it opens, then blow out as hard as you can and it seals tight. But the real proof is that it stopped the vac psi build up the instant I installed it. Cant imagine why you got so many that didnt vent in as they should, but claiming they are all crap isnt true, mine works great.
Im sure you know this, but these types of vented caps Im referring to are only used on the unvented completely sealed tanks like they used in 1970, the caps used on later year emission cars with stand pipes & charcoal canisters are different.
https://www.rockauto.com/en/moreinfo...t=5900&jsn=608
Sorry for the highjack, just wanted to reply on the vent/cap comments with info that applies to teh OP's 2nd gen bird. Back to the Tanks inc install..