Would it be possible to use a Dremel tool and make new holes 90 degrees away from damaged area in brass ring?
If so, then use 2 strong nails/drillblanks/etc. set in a vise at the proper distance and set the head of the flashlight down onto the nails and turn the head with big lock jaw pliers. Maybe with rubber gloves/intertube as a protector from damage.
Just a thought.
EDIT;
I do have one off these, series one, forgot it was on hand and I now see just how small those cuts are in the brass ring. No real room to drill holes.
Bad design from a modding and or service standpoint.
Still could try new cuts and maybe one of those ring pliers that expand when squeezed.