I have recently started getting the front wing rust. After a long and protracted argument with VW, they have come back to me and refused to pay anything as the previous owner of the car has already had the wings repainted by an indy garage. I went to my local car body shop, who i trust and has carried out a number of wing repairs.
he took me to the scrap pile and explained about the wings and the number he has done on VW and Audi as well. In the scrap pile he had a number of corroded wings. The issue is the big piece of foam that is attached to the inner wing. water collects in it and rust forms.
He replaces the wings leaving out the big foam piece and has had NO issues from previous customers, however he has had a number of people coming to him who had the repair previously by VW, who leave the foam intact.
He stated that if VW replace your wings and they leave the foam in, then you WILL have rusty wings again in the near future. He also said that the issue is so big that the insurance approved wings fit perfect as they are producing so many of them.
For me i have no option with VW so will be replacing my wings myself. I will make sure the foam is left out.