I have more dings and scratches than it's practical to mask and spray. For example, the very rusty bottom end of one of my hatch shocks popped off last night. While I fumbled around in the dark to get it back together so I could close the hatch and go home, I scratched the paint in multiple locations. The driver's door has a few mystery scratches, one of which has steel showing through, etc.

 

Ideally, I'd have a nail polish bottle full of tough, greenish paint I could use to cover these gaps in the paint before they turn to rust. Any thoughts?

go to your local automotive paint store and get a touch up bottle of the color code of your car,its about 6 bucks. ed

I've never used that stuff. It's $6 for a half-ounce, but it may do the trick. Of course, they don't make Subaru green, but Chevy Green will look better than rust.

 

I was hoping for some kind of brush-on enamel or something that bonds well to metal, and that I could buy by the pint or half-pint.

I don't have much experience with paint.