Hi, Frank:
I have taken a close look at the base of the intake and I could not find any cracks, so it is a bit of a mystery as to why it had such a bad leak. One clue, however, is that the coolant gasket on that corner of the intake was loose enough to fall off of the intake the minute I lifted it off of the engine! The gasket was still in its correct slot on the bottom of the intake, which should have been enough to hold it in place when the intake was still bolted onto the engine. But since the gasket was loose enough to actually drop off of the intake, I am guessing that it had shrunk or warped due to the engine heat and had lost its shape, and therefore lost its ability to seal the coolant passage. I haven't yet thrown away the intake that I removed from the engine because I want to really take a close look at it to see if maybe there is a crack that I hadn't seen yet. If I find something I'll be sure to let you know.
By the way, I took photos of the intake replacement process. Let me know if you want them.