Hi Alan, I think Dazz has got it right. Read this on the net. Does this sound like the problem. ( Quote
What is white worm on alloys?
All BBS alloy wheels which are diamond-cut with a clear lacquer finish are prone to what's called 'white worm'. Even with regular washing and maintenance, the inevitable stone chips or slightest kerbing can break the lacquer seal and moisture can ingress and the white worm will start and slowly spread.)
There are numerous articles on the net concerning white worm and illustrations that look like your wheels, also some suggestions for repair. Hope this helps.