slanty surges at stops?

Sounds like you have a lean condition. When it does it again, close the choke slightly by hand (air cleaner off) and see if it smooths out. Another test is to flow propane (not burning) around the suspect air leaks and see if it helps. That never worked for me when my slant idled bad, but my problems were in the Holley 1920 carb.

I don't understand why the mechanic is speculating. Why didn't he/she fix it right there? It takes ~5 min to change a carb gasket and I don't think the gasket is specific to your car, so should be easy to get.