When you push on the firing pin, do you see it coming out of the firing pin hole? Did you replace the original firing pin in your rebuild? IIRC, SA uses a smaller diameter pin than normal for their .45's.
I agree with JonM to a point that using a pen is a bad habit for the most part. I have and use a pencil with a good eraser for diagnostics of a problem only.
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Former President of the ECPT (Eifel Combat Pistol Team)