i have to join the club on this one,,,,,my dt keeled over when i was loosing air in the rear tire,,,,,fortunately it fell on a long rubber lawn chair so i escaped any serious damage....but the(left) mirror was coming loose after riding every week or so....i resolved it by placing an open ended lock washer between the silver nut and the immediate below(which holds the whole mirror armature to the scooter) big . black coated brass nut.
the silver nut when loosened allows you to move/adjust the mirror itself up and /or down.....seems to be holding