Just been out checking my tyre pressures and noticed that I've lost 6 wheel nut caps and that most of the rest were working their way off too. All are for the standard bolts - the caps for the locking ones seem to be a better fit. Looks like they need something extra to hold them in place. I remember my A3 having a substance a cross between chewing gum and blu-tack smeared on them for this purpose.