Lester,
I have made about 200 cartridge pens so far. I make them both with finish and without depending on the customer.
After trying many brands and types of lacquer, I found StayBrite Brass Lacquer (from Woodcraft). Most lacquers will not stick to brass without primer or they will peel or flake off. I have been using StayBrite for over two years now with no complaints from my customers. I have used the same cartridge pen for over 9 or 10 months with no peeling or flaking and the coating has not worn off either.
If you decide to give StayBrite a try, be sure the cartridge is CLEAN, CLEAN. I wipe my cartridges with acetone and then handle them with gloves. If you touch them with a finger, the acids will leave a visible fingerprint under the coating. It may take a few days for the print to appear, but it will.
Hope this helps