I'm pretty sure it is every Impreza RS owners fear that one day they will have to battle rust on either the quarters or roof. I bought my Impreza with a single rust bubble above the windshield, knowing that one day I would fix it. The rust was spreading along the windshield and I knew I couldn't put it off any longer. So I decided to pick at it and give myself the much needed motivation for the project.
Sand paper 36,80,180,220,320,400. Long board and DA style
Polyester filler ie. Rage Gold
Angle grinder with 36 grit
High build primer
Self etching primer
First call your local glass company to have them remove your windshield. Depending on the company this should be about 60$. I didn't realize the extent of the damage until the windshield was removed.
I used an angle grinder with a 36 grit disk to grind down all the rust and removed any remaining windshield adhesive. I also used a die grinder to get into any spot the angle grinder could not. Be careful not to grind the metal too far, or use excessive force; this causes heat which can distort metal. After all the rust is ground down it should look similar to this.
Luckily the rust on my car didn't create any holes that needed to be patched. To prevent the rust from coming back I used "Naval Jelly" over all the bare metal.
Now for the fun part; smoothing the grind marks and repairing dents. I am assuming that the hood flew up at some point in my cars life, causing the dents on the roof. First thing I like to do is outline any damage in sharpie.