I posted this question in the gunsmithing section and got one reply. Hope I am not boring you with something you looked at already Just received my The Complete Glock Refrence Guide and decided to strip and clean my slides. All three of my slides were purchased used and I have no idea if they had ever been thoroughly cleaned. My 27 was dirty with metal shavings and what I expect is the typical crud. My 19 was identical to my 27 in terms of debris. Now when I stripped my 23 something was different. I noticed deep in the firing pin hole debris/metal flush against the bottom of the hole next to the firing pin slit. After inspecting the firing pin there is noticable wear in the area the firing pin safety engages the firing pin. My first thought was milling debris never cleaned out but after thinking about it I assume the firing pin safety is wearing the firing pin. This was purchased used so I have no idea of round count. Does not appear to have been through the ringer. FWIW I have used a .357sig barrel and ammo. I can't imagine it making a difference but I have been suprised how dots are connected. It is a 3rd gen. 23 Of course I will replace the safety and firing pin. Just joined the GSSF and can't wait to take the Armorers class. Trying to gain Glock knowledge as I think we will be sharing the same space for awhile.