How I missed this post I'll never know
If you have the Hehr vents, they are square aluminum with a plexiglass plate on top. You basically did the right thing by using the vulkem. However regular pop rivets are not water tight...they have a little hole down the middle
so you have to cover them with sealant. The rear bath vent (if it is the one I think it is) is a standard RV item and should be available at most RV parts centers or via mail order. The vents not closing evenly is caused by a couple of things, one they are binding, something like WD-40 on the pivot points may help, if it doesn't they may well be bent. FWIW I am going to replace at least 2 of my 3 vents with something a bit more modern. Don't forget to take care of your plumbing vents while you are up there, they are a quite often overlooked major source of leaks, then on to the awning rail!