Water coolant leak!!

you may want to check the EGR coolant too.. is right above the compressor

 

I agree with the hose fitting. The only sealant that kind of fitting should ever see is teflon tape wrapped around the threads. Nothing else will work. And the U shaped hose does seem like it has seen better days.

 

There is a good chance that the head gasket on youre air compressor is leaking pretty common problem with d12 twin piston air compressor like the one you have check if u have pressure in the cooling sustem sometimes they put air psi in the coolant as well also there is a small gasket on the thermostat pipe right on top connects on the head and top of radiator sometime they leak from there if u dont see nothing dropping down from there then 100% for sure youre air compressor leaking internally on d12 i have seen this almost on 8 of ten truck that come in with that air copressor its just a matter of time