For small pits and imperfections, plastic filler (aka Bondo) is the correct tool for the job. The stuff they make now is much improved over the stuff from 20 years ago.
If it's over 1/16th of an inch, that's where you get into trouble. It ain't dent repair, that's what hammers are for!
You could try solder, but there are problems with the resin causing paint to lift. If the pits are large, you could weld then grind. In the end you may require a wee bit of Bondo anyway.
-Boyo
