I would primer the bare metal just to be safe. If you have spray primer just spray it into the lid and then put it on with a brush or q-tip or toothpick. If the touchup brush is too large, as it sometimes is, you can use instead an artist brush. They are available in all sizes, cheap at Wal-Mart, etc. One of the keys to getting the paint on is the viscosity. You can thin it to make it flow better, got to use the right thinner though, laquer or enamel, based on the paint. On a flat surface you can really thin it and it will flow to fill up the indentation. More coats if neceessary. Sounds like you're on a vertical surface which is a little tougher. Lay it on at the top and let it flow down, working it around a little with the brush. The paint will shrink so you may want to put on more than one coat - maybe two weeks apart. Some people overfill slightly then sand with a tiny sanding block and 2000 sandpaper. Again you've got to let it dry for weeks because it's going to shrink for quite a while. This all has too much waiting time for a detailer. They will usually fill the depression and then wipe it level with acetone.