Hey Chris
6018 is also very "nervous" in terms of response to the steering wheel. It darts left or right just as you've described. I have to really "focus" when I'm driving it. In every other way it handles beautifully, and tire wear is very good. It is unbelievable in the way it attacks corners. It has the stock 3 degrees of caster.
I've always felt it needed twice as much caster. Could the issue simply be toe-adjustment? I'll be watching your thread for developments. Hard to believe a "steering rack replacement" and "re-alignment" brought about your change.
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