That's some fine troubleshooting. I'd never think to look for a broken slug.
I received kbmuri's inner brown knob and it's a great color match so I've got a complete set finally
I hooked up a test pattern generator and have been tweaking the picture.
This is what I have so far. The squares are larger in the middle than around the edges. I can make the top or bottom rows larger with the vertical linearity, but I need to make them both bigger (or the middle smaller). I've been fiddling with both the size and linearity and this is the best I can get.
Any thoughts ?