Well, in the absence of any advice bit the bullet and sent the wheel to Perfection Group at Whetstone, Leicestershire LE8 6NU. Saw them at work with their mobile unit at the local VW garage when they refurbed some 'normal' alloys on cars going onto the forecourt. Not the cheapest quote so hope they get it right! Will provide an update in due course with pics if I learn how to do that.