I have a 2 letter prefix (1989) model 19 that occasionally fails to fire. It will dent the primer but not detonate the shell. I would appreciate any advice on what parts to buy that may fix this problem. The pistol was updated by Glock years ago. I am really thinking of replacing everything in the slide. Is this worth the cost or is the money better spent on a new 19? This pistol is in very good condition otherwisw. Thanks to all.