So you are grabbing that tab at the bottom of the rubber straw to pull it into place? It just clicks aka pops into place, no key slot alignment? Have not gotten it out yet, a bit hard yanking. The instructions have no words, but you do need to rotate the straw up, open first, like you do, or it is harder to get off when you pull the locking pin, tab out. Got mine jammed a bit sideways without doing so, the first time, pressure from the straw on one side, causing it to jam up. And I missed that the straw has one way to go in properly, the end with the intention ring goes into the lid. Yes it's on the diagram instructions, you just don't notice it.
So you don't have to take the little silicone stopper out, like you do with the Sport Caps? How do you clean under it? I was just trying to take mine out & having a really hard time of it, so I thought I'd check the official Klean Kanteen video to see if they took it out, & I didn't see them do it, either.
There is a silicone gasket between the top and bottle. Have you checked that? That air valve comes to mind too to check. Maybe a good soaking in warm water and vinegar? ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-oOMQepEecq8.html