00 GT-S alignment gone bad

[Jfo]

Get ready for an epic journey, I can tell this will be a long one.

Brought my 00 GT-S in to Sears (My first mistake I know) to get 4 new tires mounted and an alignment done. After taking 3 hours to mount and balance the tires I overheard some of the sales staff discussing my car so I poked my head out of the waiting room to see what was up. I was told, in a very unapologetic manner, that the "mechanic" sheared off my left rear cam bolt trying to adjust that wheel. I was then presented with said sheared off bolt. Actually the guy sheared off the nut end that faces the rear bumper when you look at it from behind the car. the whole thing was rusty, but it was pretty obvious that some excessive force had been used, most likely an air wrench, and no chemicals were used to try and loosen it. I was then presented with a work order with a hi-lighted price of $368 to replace the knuckle and the bolts. naturally, I said I saw no need to pay for something that they broke and the sales kid said it wasn't their fault that it broke, it was rusty. Talked to the manager and got the same story, but at least he tried to find me used one. I still don't believe I should be responsible for their ineptness.
Long story short they welded it so I could still drive it, who knows for how long so I am driving like a little old lady. After doing some research I don't think I should even have to replace the knuckle, shouldn't I be able to get the rest of the old one out of the knuckle and replace it with a new one? Looking at where it was welded they didn't totally cover the bolt hole so I should be able to grind that away. Just in case I did find a new knuckle online for $100 less than they quoted me.
Anyone else have experience with this? Any insight on whether I have to replace the knuckle or not?
Come Tuesday I will be making the hour drive to my nearest Toyota dealership, where I should have gone in the first place, to get a second opinion.

[Bitter]

http://www.jegs.com/i/Prothane/311/18-302-BL/10002/-1
that kit will have the bushing that the bolt is seized into, you can only break that bolt with a BIG LONG breaker bar, not an impact gun. You torch the old bushing out and install a new bolt with new nut and new cam plate nut. should cost about $30 from the dealer for the bolt, plate, and nut and all but the nut will have to be ordered.