I'd take it back for an exchange -- for another brand or remanufacturer. Who knows what the results of that loose bolt would be even if you torqued it correctly -- fluid/air leak?

My understanding is that they're supposed to be pressure-tested after rebuilding/reassembly. Clearly, this either wasn't pressure tested, or it passed simply by luck; or maybe there's some minute debris under the head of the bolt that you can't see that's generating the pressure (between bolt head and caliper body) to seal it right now, but who knows how long it will remain intact.

In any case, this certainly doesn't speak much for the quality control of the rebuilding outfit.