If I hadn't opened it at the store (which I would have almost certainly done), I'd be taking it back to him and letting him replace it ... and why not? ... after all, IT is going to replace it for him ...
you've gotta give the merchant a chance to make it good ... goodwill is his most valuable, but least tangible asset ... he depends on your goodwill and that of other customers to do well with his business ... if you get (ticked) off and don't do business with him because of it, you both lose ...