If returning it isn't an option I would say go shoot it. You don't want to go messing with the sights if they are gonna work as is. The loose tube may cause some feed issues but you won't know till you try. After you shoot it. If you need to you can bang the rear sight over. I can walk you through taking it apart and we can get a better idea of exactly why the tube is loose and how to fix it.
I don't need No stinking signature.