I've not seen this in other threads. As shown in the pics, there appears to be a leak of some kind at the rear of my intake manifold. I've been losing a small amount of coolant, and only been overheating when on a long trip, or the engine has been under stress for a bit. The radiator, water pump, thermostat, fan clutch, etc have been changed. There are no visible leaks anywhere I can tell. Have not ruled the head gaskets, but the leakage is so small, I'm hoping it's something else. Any ideas?

 

here's some close ups