I had a small but persistent coolant leak not long ago and spatter was exactly where you point to and it turned out to be a pinhole leak from the radiator, just below the upper radiator hose where the plastic meets the aluminum. Found it via pressure test like Hummerz suggested.

 

Appreciate the response and great timing actually. Everything was good when I bled the system last night and also this morning. Drove it home from the office and got a faint smell of coolant when I got out. Ripped open the hood in disgust and lo and behold I see the same coolant spray as before. Looked around a bit and noticed this leakage in the same area you mentioned:

small leak in upper left of radiator

I had suspected the radiator a few times throughout this process but couldn't ever pinpoint an exact location. And on top of that, I watched drop after drop of coolant drip out from around the bottom bolt of the water outlet last weekend. I lost nearly the entire amount of coolant in my reservoir tank (filled up to the fill line) in one 15 minute drive and all of that did not leak from the top of the radiator. Bottom line is, the pressure test recommendation from @hummerz should have been the way to go first.

Bought the radiator from Rockauto in July, so guess it's time to figure out how to go about getting a replacement under warranty. Thanks again for all the replies and suggestions.

 

There is a rubber gasket that fits into a groove on the bottom of the housing.

 

I've gone through several radiators the past 3-4 years. Not with the hummer, but other vehicles too. Mahle radiators specifically seem to be notorious for busting in a short period of time.

 

More wrenching on the way..........