I have a separate thread on this board about it. I did a leakdown test and did not find anything. So I decided to replace the radiator first and then do a CO2 test. It cost me about $500 in parts (all hoses, thermostat, temp sender, Honda radiator fluid) and now everything is running fine. I've driven up the Camarillo grade at over 100* outside with the AC going and I got no heat problems. More importantly, no CO2 is showing in the test.
I now think the dealer was completely lying or totally incompetent. Now that I've done the CO2 test, I can't remotely see how they could do the test with a cracked, empty radiator.
Here's to another 100,000 miles!