Hmm!!! I've had duff M/Cs from Brakes international as well before now... Mine had obviously been sitting on a shelf somewhere for some time and the seal blew on the first pump, and an MX-5 rear caliper which failed a week after I fitted it. I've also had a lot of gear off them over the years that's been fine and there prices are usually better than anywhere else.
Still very frustrating though.
Had you not solved it i was going to suggest you checked the rear shoe clearance. Remember self adjusting rear brakes means you have to adjust them yourself
At least you've got it sorted
BV.