Hopefully one of you BMW diesel guys can help me out. All 3 of you. I just refilled the DEF tank on my 2016 BMW 535d, but when I reinstalled the DEF cap, it is not clicking closed, and it's very easy to unscrew as it is. I think it is supposed to click when tightened, but I'm not 100% sure; I don't remember from the last time I filled it. I don't want to risk breaking the cap by overtightening it. Any help is appreciated.