The one that told you negative caster is wrong, positive caster gives you stability. nagative caster porvideds for easier steering, but is unstable. You don't see negative on too many cars these days, last time I did one that was negative was a '66 Thunderbird. Needed to be nagative because of how for forward the engine was. It wouldn't steer other wise.
I, too find overboost unlikly, as the box and pump are matched. I would test the pump before condemning it.
If the dealer won't warrantee the alignment, get you money back.
BTW, I've been an alignment mechanic for almost 20 years, and am a Certified Master Mechanic..
