Thanks Irish Dave
I tightened the barrel latch screw up, and it helped (it was loose - probably from the recent cleaning).
It still wiggles just a tiny bit. I'm no machinist, but it sure seems like there is the tiniest gap down where the main hinge is. If you're just holding the pistol, it doesn't seem to move, but if you hold the barrel and the grip, you can feel it.
Ideas welcome. Thanks