Oh man...
after all that!! I hate O-ring sealed metal/solid coolant lines. Went thru a similar situation with a ford car years ago. If either ends of those pipes is out of round, they wont seal. You might find thicker O-rings in the hardware department (home cheapo, slowes, etc..) but it *may* cause fitment issues. A good RTV slathering might be just what the doctor ordered.
G/luck
Joel