Head bashing smilie here... I'm betting some of that crappy caulk is silicone
Pull the vent out, scrap all that crap off and reinstall using butyl. You may want to add a self-leveling caulk around the outside over the caulk (or maybe not).
But, you've already found out adding more caulk to something that
leaks doesn't help for long on an all-molded-towable. DANG.