As many of you know rust and crxes is like white on rice. When I was redoing the exterior of my car and getting it ready for paint I had the usual bad spots on the car sunroof, lower doors and 1/4s. One thing that worked for me is Por15 I used the silver formula on all of these spots and rust has not come back. I sanded the lower doors down to the maetal and applied on both sides and no problems same with sunroof and 1/4s. Check it out theres many products from them and use them step by step as the instructions say.