Tim Greif - West of Chicago
One of my hobbies used to be brass restoration. I've used nitro-lacquer, acrylic lacquer auto paint, ACE brand spray lacquer, spray poly and clear spray from Rustoleum and Krylon. I learned the techniques from an old gentleman in Iowa that did restoration for a living. He used a dipping tank full of what he called "bake hard enamel" that he bought in 35 gallon drums. He said it was the best thing he found to seal the metal and still be flexible enough to withstand dimensional changes as metal expands and contracts or flexes. He recommended I just use spray lacquer.
I found the Rustoleum spray clear would last about 2 years before it developed a "craze", essentially tiny cracks in the coating. My best success was with quality automotive acrylic lacquer which needed to be sprayed with either a detail gun or air brush. Kind of a pain for small jobs.
Next best was plain old ACE brand spray clear lacquer. Good performance and no "crazing". Others have mentioned cleaning of the metal. I concur. I simply cleaned everything with lacquer thinner and avoid touching any exposed part to avoid fingerprints.