There is a stamped part-circular metal plate with a hollow lug/pin that engages with the retaining handlebar hole, screwed to the plastic start stop assembly. The aluminium handle bar hole over time enlarges a fraction of a mm, maybe 0.4, and the whole assy rotates considerably. The grip removal is necessary, else you can not remove the metal plate from the plastic, as one screw is obstructed by the bars. However rather than take off the cables from the grip, I ended up creating enough slack to pull the grip, cables still attached and all, off the end of the handlebar. The hollow lug in the metal plate then received a blow from a tapered dot punch with a hammer, thus flaring it a miniscule amount, and all the play at the start stop assembly is now gone.