No, I haven't tested a zz yet. I don't have one
I know the local rs that I go to most of the time doesn't have any. They have like two body sets, but no cars. Maybe I'll start checking the other ones around town to see if they have any.
If your car was going in circles, I'd bet you missed one side of the spring when you put it back together, not that the magnet was too strong.
Yes, sanding and polishing the steering arms/pins did the most for me too as far as helping steering action.