I’m trying to figure this one out and since I have no experience I’m hitting a dead end. I’ve googled the hell out of it and it’s pretty much always “buy a new one”.
My main question, should there be a rubber washer in there? That seems like a spot that would have one but I honestly don’t know.
It could be a faulty valve again. They are junk, and it’s not remotely unheard of to pop in a new valve and it immediately fail. I know it sucks, but at least they are cheap, and if you bought it off Amazon or something, you can probably return it.
Source: Recently purchased a motorhome with a leaky toilet intake valve. Replaced it and it’s still leaky.