Usually if the screws in the bayonet mount loosen you'll have trouble putting the lens on your camera. I just had to tighten them on my 70-200 (it pays to have a jeweler's screwdriver in your camera bag!) and it was obvious one or two of them had loosesned because the lens didn't want to rotate and latch onto the camera.
There's almost no play in my 1.4X II... just a tiny wink of play axially in the bayonet mount when it's latched onto some lenses or cameras. It's a tiny bit on each side, hardly enough to feel... seems normal to me.
Still, it wouldn't hurt to check the bayonet mount screws, four on each side. The only other screws you can access easily are the two holding the trim piece around the release lever and those shouldn't be prone to loosening (plus they are painted, so I'd be reluctant to apply a screwdriver to them unless I could see one had loosened).
If those screws loosen on you a lot, might want remove them one at a time and put a tiny dab of blue LocTite on them. That's the lightly holding LocTite. Don't use the stronger holding red stuff or anyone servicing the lens in the future will really curse you!