I was fooling around with my IR thermometer the other day, and pointed it at the cool exhuast manifold just after cranking up cold - it was all cold until I got to a spot on the edge of the gasket and went to 450 degrees, and I put the Mark 1 palm reader down there and felt it the leak. Just another tool in the box.... but would work best when things are cold.

 

To close this out. I found the leak. The weld on the downpipe-to-manifold flange cracked. Welded back up, all is good.

 

My '95 cracked there as well. But since I had close to 200k on the original cats and they'd been rattling for a long time I just replaced the Y-pipe.