Screws coating has come off , what to replace it with ?

greetings members , i have noticed lately with Controllers or MVS carts i've been working on either rust or a white substance. I have cleaned it off in a lemon and vinegar bath or a CLR bath , but i noticed that the previous coating has come off leaving it exposed.

i'm thinking buying some sort of spray to protect it so rust and corrosion comes back , any tips ?