I've had an issue for a while now, where my toilet seat gets loose and starts to slide side to side after a little time.

Here are some images of the style of attachment the seat/toilet use, basically the black bit goes into the toilet, there's no nut on the underside as seems to be common, you then tighten the screw to make it grab as it pulls up the nut hidden in the black part.

The issue, I think, is that the part I've circled in red, is what the seat actually attaches too, and it's a separate piece to the part with the black insert and is only held in place by the same screw that goes into the black piece. It's meant to have some adjustability to account for different seats etc… however, no matter how tightly I do up the screw, after a few days to a week it will, I assume, work it's way loose enough to allow the grey disc/metal post to spin/move.

The only option I've been able to think of is doing something like using a thread locker on the screw/nut that goes into the toilet, but I'd like to avoid that, if at all possible, as it will make changing them very difficult if I ever need to do that in the future.