They say it is best not to orally moisten the tip of your brush when you refurb your sights.
True, but one does not need to moisten anything at all. Grind a few granulae of old radium paint [under some inert solvent, like alcohol, so it does not dust], let the alcohol dry. Make some epoxy, smear it on one side of the sights glass inserts. dip each insert in the radium paint dust - it would stick to epoxy. allow to dry, and then cement the insert with the paint glued to one side into the sights cavities, so the paint is not even exposed, but is covered with glass at all times.