SO their logic goes like this? "We have multiple machines with the same defect. Ergo, we aren't going to swap out your defective machine. Your $1,300 doesn't buy a proper fit and finish. You are being too picky, sir".
Is that the gist of their attitude? With an attitude like theirs, I'd be developing a major attitude of my own! I'd get satisfaction one way or the other. IF you paid by credit card you could contact them for reversal of the charges until this is hashed out properly, in which case I expect the result will be you will get a properly assembled MB.
Keep us posted, please.