Also, have to say that I honestly trust the OPs sense of smell more than the pressure test. It's possible that when they pressure tested it that they didn't have the heater on and thus, I think, would have failed to pressure test heater core.
It could be another smell, I suppose, or they didn't really hold the pressure for all that long to see a small leak.
Performing at the Comedy Cove--595 Morris Ave. Springfield NJ reservations 973 376-3840
A recent set
dmax on the radio every Wednesday 7-9 p.m. NYC time. Call in! (661) 449-9340 watsonnwatson.com