One Shot is for use in sign painting, and as such it has good coverage (as the name implies), and is self-leveling. It is also meant to be durable and weather well. Properly applied One Shot should hold up to the solvents you mentioned at least as well as the factory black finish on the frame of the gun. As with all painting, the prep work is important, but, in this case, not too difficult. Just remove all of the oil and grease from the sight (be sure to get into the serrations), and dry it completely. Some denatured alcohol on a cotton swab should work fine. Make sure there are no residual cotton fibers in the area you wish to paint. Also, apply and cure the paint at room temperature or so. High temps will cause the carrier to volatize, leaving bubbles in the paint that will allow it to flake off easily once dry.
Once cured (16 hours or so), it should withstand many cleanings and holster presentations. And if it does begin to wear a little, it's not a big deal to dab some more on. Show us some pics of your handiwork once completed!