Here is the end of the other metal coolant tube that runs along the top of the block. One end goes to the heater core, and the end you're looking at connects with one o-ring to the block just below the thermostat housing. The o-ring at the end of the tubes just crumbled in my fingers. I had a leak here, and these tubes are not accessible without removing the intake manifold, etc.... You can see the pool of coolant between the heads in the second picture.
I wonder if the 98+s have the same design.... If you have a '97 or older, I imagine this leak is imminent. This is not a fun repair.
I might add that Joel nailed the problem from the first post I made on the subject. Thanks!!