I did some research on this problem and rather than try to put it in my own words (which I'm not good at because I'm an engineer and not a writer) I'll just copy the information and the links below.
I don't expect Laco to fix my problem but at least I learned something new!!
This is a typical problem. The laser etched area is the weakest area on the parts and must be passivated to prevent rusting in the etched area. However, it can be very difficult to get the etched area passive without removing ALL of the darkened color used for identification.
We have had great success with our citric acid formulations in producing excellent corrosion resistance in the laser etcehd area without removing the color. Many surgical instrument companies have gone to this sytem because the amount of problems and rusting are significantly reduced compared to nitric acid passivation.
Can CitriSurf products be used on laser marked parts?
Laser marks are very susceptible to corrosion if they are not passivated. One of the best properties of CitriSurf is its ability to get good corrosion resistance of laser etch marks. Depending on the laser settings used, CitriSurf may fade or remove the black mark. If this happens we recommend higher power and depth of the laser mark If this is not possible, we recommend a full duration passivation of the part before laser marking, and a shorter duration passivation after laser marking, thus restoring as much corrosion resistance as possible without fading the mark.