Minor bodge. Currently using a C&B Seen rear light, attaches with an O-ring. The place I liked to mount it was on the bit of seat tube that sticks up under the seat clamp, but here it would rattle against the seat clamp plus it would twist around somewhat. Stuck a little cushion made out of Sugru on the back, made an impression of the seatclamp in it, then let it dry. Much better now.