I asked a question about this a couple months ago but the problem still persists. I have a 24C and only fire factory ammo out of it. On the right inner part of the lightning cut there is grey residue/missing tennifer. It looks like it's down to the steel of the gun but I'm not sure. Is it possible that the heat from the ammo melted it off? I tried a steel brush with CLP and it didn't help. Now I'm worried that it's prone to rusting. If I called Glock would they be able to help? Thanks.