Hmm I have buggered one up , 3mm key just spins in it, other seems solid and loath to touch it now.
I feel a trip round the local garages coming on
It was definately a metric allen key to undo mine, which is what I would have expected since its not part of the engine.
The impact driver suggestion would be no good as the headlamp is too fragile not to mention bulb within.
Had a look at mine this morning and it looks possible to get mole wrench adjusted to grip tightly on the outer part of head allowing twisting undone after liberal WD40 treatment, and without damaging rim. Just need to source a fresh screw then - suggest stainless.
