Originally Posted by Hirnbeiss

A quart an hour is a big leak, especially at idle, and I can't say I've ever seen a torqued-down headgasket leak like that (not that my sample size is all that big). Plus, your mechanic already re-did the gasket and nothing changed.
1. Believe your indications (lesson learned from 3-Mile Island)
2. Doing the same thing but expecting different results is (used as) a definition of insanity.
The 3rd thing is that replacing the radiator (with oil cooler) will only run you about $200 (recent auction site offer) if you do it yourself.
DIY
I would do that before looking further at the headgasket and block.