I have a pretty nasty sun damage that has grown since the start of the fall here in the US northeast. The car is clean on all other accounts but there's a big white/steel colored spot on my door panel running up the side where it meets the back door. What is the best way to patch paint that? Should it be professionally sanded and fully repainted or will sanding the effected area and taping out for a small paint job pass? Never done much exterior maintenance before.