In my S1 I noticed rust flakes to fall out of the roof whenever I opened the sunroof. So I new trouble was coming up. The sunroof was taken out, a torch lit and....what a mess.

As far as I could see there was only superficial rust.
I took a small steel brush and attached that to a stick. Then I rubbed down all of the interior of the sunroof cavity. What a ridiculous construction by the way, no ventilation at all, so such an area is prone to rust.

After that I hoovered all the rust flakes out. Next step was to treat the cavity with Fertan, a product that turns rust into a neutral black surface. This was after I covered the interior with an old bedsheet, you never know if there's a leak somewhere.

After that dried, I put in a nice layer of waxoil and lets hope that's it for a while.
With the waxoil dripping to the floor out of the tubes in the back of the roof, I knew these were open.

Not a nice job was putting back the sunroof, first cover the roof laquer, otherwise you will end up with scratches!!

Cheers.