I have no idea what is going on with your vape. Too many variables. I might (gently) suggest that if tossing a bad cartomizer (and if you have a third, new one, I would try THAT one) is "way too expensive" that you consider a different type of setup that might be more cost effective. Cartomizers tend not to be, but especially since you just dropped your vape in water, perhaps a slightly newer setup (I'd suggest a MTL atomizer coupled with perhaps an internal battery if you want to keep things simpler, maybe a setup like and Aspire zelos mod with a Nautilus 2 atomizer that you fill and vape, but you are only replacing the coil, so it's less costly over time) might be the way to go?
I'd also suggest taking your setup and some cartomizers to a good vape shop if you have one near you, that might help in trying to isolate exactly what the problem is. It's possible you have an electrical fault in your mod that is intermittent, it could certainly be the 510 pin, since you dropped, depending on how much force, it could have gotten "wonky" somehow, or it could be a bad cartridge.
But as of right now, I have no idea what the problem could be. If the vape shop can't help, you'd be looking at another vape anyway, it might be useful to consider other options besides cartos, especially if "your carto" (again no idea what it is) is "that expensive."
Best of luck I hope you either get it sorted out or move on to something better suited for you. With that said, if this is your preferred way of
vaping, you may need to look at repair or replace, I'm sorry to have to say.
Best of luck,
Anna