I doubt the coat is thick above the lock, most often brass parts are laquered with a special lacquer, without acidity to avoid future tarnishing.
Small polyester cracks can be repaired and polished without laquering the whole part. (with Koenig repair kits ) It must be difficult to do that cleanly around a lock, however.
I cannot say there but the lock may be accessible from the underside
The Koenig polyester is usually an undercoat , but can be poiished to an almost invisible joint. http://lakeoneusa.com/index.php/categories/konig-finish-repair
The problems are micro bubbles (heating lightly the resin , mixing it slowly in its can by turning it slowly, and allowing enough time for the air to escape after mixing the 2 composants helps well to avoid the bubbles)
Last problem is the amount of black dye. 2 to 4 drops is maximum, or the hardness is not enough, here again, the concentrated dye sold by Koenig does the job.
Water sand up to 2000-3000 grit (on foams for the last ones.
I have read that polyester primer have to be sanded without water, but I suppose it is only for the products used in automotive to close defects, they may content some powders and adbsorb water.
The repair poly is sending some parrafin at its surface. this one have to be cleaned before another coat is added.
Cleaning the side of the repair (cut in a dish shape to obtain invisible joint)with acetone helps me to avoid a greyish line. I suppose that polyester solvent would be better but I dont have it)
I would mail to the factory to ask advice (and let us know !)
Those sanding disks are invaluable :http://lakeoneusa.com/index.php/products/abralon-sanding-disc-360