I was lucky to find this, I failed to see it during my actual testing and not until I started rinsing of the soapy water bubbles starter appearing on one of the lower corners. On closer inspection it looks like the leaking tube had been deformed from the radiator being dropped, but as there was no apparent damage to the tank it could mean the core has been dropped before assembly. Coming to think of it one of the mounting flanges was a bit bent in transit, maybe the tank has taken an impact and passed it along to the core?