I haven't actually located the point of origin. Caught this last night. Didn't have a lot of time to pursue.

I agree with your hot-spot idea. I'll top it off, run it again , shut it off, pull the shroud, then feel for hot spots.

It leaks with or without any pressure in the system, so it might be easier to find by simply pulling, then fill with water. I would be easier to see the radiators entire surface out of the vehicle. If the surface is cool further down, I may just go ahead and get another radiator.

I just got off the phone with several local radiator shops. Over-all, they seem to believe I have partial flow. Interestingly enough, it does not overheat on the highway, or at idle.