Bob,
I think it kind of depends on how big the "pits" are.... You should be able to get the little ones out with filing and sanding, although I confess, I typically don't sweat little ones, as long as there aren't tons of them.
If you have something bigger, like a casting flaw, you can fill them with brass colored solder, such as used to repair brass music instruments. Do a search here, and you should get some good info on various techniques.
Ed