I tried my VW dealer last week... Got the ole "oh I've never seen that before" crap... then told me my best bet was to go to the VW body shop (30 miles away). Really not helpful, and you could tell that they've had the issue MANY times before, because after a few mins of discussion, he told me what causes it
I phoned the bodyshop, and they said to go to your local dealer.... sigh...
I'm tempted to grab a wing off ebay and get it painted, fit it myself, probably circa £80 all in.