Okay, I found the problem...

I'm not sure what it's called, but it's leaking out of the top of the catalytic converter, where it connects with the back of the manifold.

There is a flange-to-flange connection gaskested with a standard exhaust gasket, then a flex connection welded on the cat. This flex connection is leaking.

It looks like I need a new cat, or a new connection welded on at least.

Is this a common failure point??