I need some help. Have a Glock 20 10mm that has recently had 3 failures to fire. The primer has a mark in the center from the firing pin but not the familiar mark of a Glock. That image is very faint. Could it be a weak firing pin spring or trigger spring or what? This Glock is 13 years old that I purchased used about 2 years ago and has worked beautifully except this incident last week. Any help would be greatly appreciated.