[lugerholsterrepair]

Matt..Welcome to the Forum! This, I am positive, is due to rust. Why? Can you see a great deal of rust somewhere?
David gives good advice..removing the top is relatively easy, even for a noviceOnce the top cannon is off the frame the toggle pin can be removed allowing the toggle/bolt to slide back & out. This will let you look closely at the insides.

I don't encourage taking the left grip off (the one on the safety lever side of the gun or you may experience the $1000 chip) Well..as long as you are a tad careful this left wooden grip should not present any problems. IF the chip happens it was likely broken during firing and just hung on like a loose tooth. I take out the magazine, stick a finger inside and gently push the backside up and away from the pistol frame. Just be gentle.