The copper helps with the gumminess.
This was a true metallurgical defect. It is, 1mm from the area, not registering on the C scale. I had to use the b scale. 2mm from the site, its right as rain. The problem was likely entrapped air in the casting that the bar stock was made from.
Disclaimer: I'm just a wealthy tinkerer, and I dont know how to make assumptions when it comes to kinematics and materials.
Then again, beer and pretzels!