In my experience, WD-40 has a nasty tendency to turn into varnish, especially in a place with no air flow. It's fine as a solvent and water displacer, but I like to follow up with either a blast of non-chlorinated brake cleaner, or if I can wipe/dip it, denatured alcohol, followed by a blast of compressed air. I just tore down my PCR and 97 BD, when reinstalling the firing pins, I just got some moly grease on my fingers and burnished it in, not even really enough to make it greasy, the moly will actually bond to the steel at a molecular level and last a long time, the grease is just a carrier. Later.
Dave