Might be worth checking for possible Electrolysis Corrosion condition.
"Radiator and heater hoses can also fail from the inside out due to electrolysis corrosion. Rubber is normally non-conductive so you would think this would be impossible. But the coolant can react electrochemically with the synthetic rubber, causing it to degenerate, pit, crack and eventually fail. If you cut open a hose that has failed because of electrolysis, the inside will usually have fissures, cracks and pits created by the electrochemical attack."
http://www.aa1car.com/library/coolin..._corrosion.htm
More helpful info:
http://www.sancarlosradiator.com/Vol.../education.htm