Originally Posted by delsol161

you can't fix rust but sanding it. it will come back. the only way to truely fix it is to cut out the metal that's rusted (around 2" from the perimeter of the rust, all the way around) and weld new, clean metal in.

however, if ya want a quick fix, grind it down till it "looks" clean, and smear long-strand fiberglass filler. however, it will come back. it's prolly inside the panel, and will just penetrate through to the front again down the road. good luck. i had to cut out my wheel house lip, top to bottom, 3 inches into the body. it sucked, but it's the only way to fix it. good luck.