When you say, "sent away for a refresh" what exactly did this guy do for you, clean up, rebuild? Seems to me if you discover a fault in any part in your care whether it be heads or block or whatever you would consult with the owner before doing any further work and subsequent expense, Bit more info required..., And if you found the crack he most certainly would have.
How long have you had the car, the concern would be what caused it, if the engine has been 'cooked' by a previous owner, and if it is only limited to the one head,