VW aware of corrosion issues with alloys and with hubs, and should replace both if required.
alloys - reason is moisture reacting with the laquer on the face of the wheel which makes it corrode. dealer will replace under warranty but check when you have the new one that it matches the rest as some have found that they are slightly different wheels, (could be a dealer error, not sure but has happened!)
hubs - again should be replaced under warranty but there is not alot of point to tell you the truth as in 6 months they will look the same, a few peeps have painted theirs with hammerite or similar and it does the trick.
HTH
