The button does unscrew, but it can't be taken off, as far as I could tell, didn;t want to pull it and break something!
Will find some washers and report back
A stitch in time: Strongly advise you fix it pronto. A friend of mine had the whole lot disintegrate whilst ready to pull away at a set of traffic lights. Not easy to find the bits in the footwell and big queues behind him!
