Should This worry me?

[NXcoupe]

POR15 is the shiznet. I am having my vert completely done underneath with it in a few weeks. Just follow the directions on the can, and it leaves a thick, glossy black coat that stops rust from continuing.
All mustangs have some rust in the welded areas, if they've ever been exposed/driven in the rain.

 

[vermilion]

aluminum pits. gray powder residue which is a form of corrosion. depending on thickness of aluminum and damage of pitting, you can lightly sand and treat it without issues. prime and rust-preventative paint. aluminum mostly pits due to long term moisture,air, electrolytes. dissimilar metals also cause this issue. IE. steel fasteners on aluminum base metals... again to OP, sand, clean, prep, prime, paint.