well, must be the hose connections if it was leaking with no pressure in the cooling system, I'm not real keen on those spring clamps, prefer wide screw clamps .... you could take the core to a rad shop and have them check it to positively eliminate that - also could use a compressor regulated down to 10-15psi [as a shop would] for a better leak test yourself, with a piece of hose on each tube using those clamps
Bill
