Gideon, After sanding and then polishing it last a good 5 years. My motorcycle engine is a 1995. Polished twice. My vans wheels were clearcoat from the factory, but cracked off in only 10 years.
Afterward I use mothers mag polish or from Lowe’s , Starbritte stainless steel aluminum polish.
Pictures below just show the piece just sanded , no polish yet or brown, white , red rouge .
This is also florida, no salted roads here . Lol.
Have you seen aluminum truck tool boxes up north? They keep rather well. I have a friend who races drag boats and his whole outdrive is polished.
If your asking about that cover, my firewall removes from the inside of the car in three sections. Left center right.
Dakazman