Forgive me - I don't have a P99 (yet) but this is a more general question and this is the most active forum. On my P5C the rear sight paint (white stripe) flaked off. Is there anything special I would need to touch it up other than automotive touchup paint?
I've not had to touch up sight paint on my P99 as yet. On other pistols I've tried model paint but it comes off with cleaners. I picked up some Sitebright sight paints at a gunshow (I've seen on line as well). Not really a paint, more of a rubberized kind of thing. Sets up over night and solvents don't seem to affect. Comes in a bunch of colors and you apply with a tooth pick. They also have glow in dark additives for the paints if you want. Buying the selection allow you to experiement with the colors to find the one that works for you.
Check out Bright Sights High Visibility sight paint and especially the directions for application at their brightsights.com web site. Application technique is critical according to another extensive article I read, which I have been unable to locate.