I've got the same thing on my '73 landyacht. It has deteriorated and cracked from u/v exposure. needs to be replaced. I need to get a price on a part, if a solid alluminum one is available. Andy only has the plastic-looking one's on his website...but those are "sale" items.
for now, I've got these silly looking vent covers on the trailer...PO installed them....now I'm starting to understand why. These probably divert enough H2O away from the vent to keep it from leaking. probably a cheaper alternative to the hours of messy caulk removal I've been doing lately...some idiot, or series of idiots just put layer upon layer upon layer of caulking around all 3 of these vents. what a mess...major pain to remove and re-do neatly. I suppose paying whatever "shop rate" is to have someone remove it would be WAY more than just paying them to cover it over with one of these things.....that's my theory, anyway. They look stupid on an AS. (I've seen 'em on SOBs, and they seem to look ok on them).
Oh, and I don't know where they're getting the "hole free" installation. 4 holes were drilled in the roof of my trailer to install these.