Yeah. I looked at manuals and took it apart. Couldn't figure it out. Just added a dab of glueIt's been 2 yrs since I messed with that light mount, but I don't recall a screw between mount and stem. Wiggled mine just now, and no left-right play.
I know you wouldn't be asking if it were just a matter of tightening the screw holding the light to the mount.