I'm restoring my 205 GTI at the moment and I'm using a Bilt-Hamber Deox gel to treat any areas of rust that are not bad enough to be needing patched. The stuff is brilliant. You basically remove most of the rust with a wire wheel first then coat it in the gel and cover with cling film. After 24hrs the gel has turned black and when you remove it your left with clean metal. I'm sure I've got some photos on a hard drive of areas that I've already done, I'll get some uploaded later to let you have a look.