easy, head gasket
There is a heater hose that goes to the left rear top side of the intake manifold and that fitting leaks engine coolant sometimes and it will run down the back of the intake around the distributor. If that fitting is not leaking then the intake manifold gasket is leaking coolant in the corners of it. REplace the intake gasket. That's all that can leak coolant on that year engine. If coolant is leaking out between the transmission and engine block then you have a freeze plug leaking in the back of the engine, between the transmission and block. Must remove the transmission and flywheel to fix it.
If coolant is leaking from the back of the engine it is most likely that the intake gaskets need replacement or a possible heater hose connection depending on the year.
The drain plug for the engine oil on a duramax should be on the back of the oil pan at the very bottom.
Heater hoses? freez plugs
1. Water pump possibly weak, failing or leaking coolant 2. Thermostat is not operating correctly or the housing for it is leaking coolant. 3. The water jacket in the engine block has possible restrictions or leaks somewhere. Head gasket breach...leaking coolant? Freeze plugs on side of block? 4. The radiator hoses (upper or lower) have issues and are leaking. What area of the engine compartment is the STEAMING COOLANT coming from? Top, Bottom, Front, Back, Radiator, Engine etc. (This info is important for anyone to be able to help diagnose the problem without being able to ACTUALLY see it).
You need to climb up and lean over the engine and run your fingers around the back 2 corners of the intake manifold and see if you get antifreeze on them. They are none for the intake gaskets to leak engine coolant. It is a common problem with the vortec engines. There are also 2 freeze plugs in the back of the engine where the fly-wheel is bolted to the engine that could be leaking engine coolant. There is also a heater core hose that goes into the rear left corner of the intake that could be leaking. The hose fits into a quick disconnect fitting that screews into the intake. It is common for the fitting to leak too,
Yes, coolant can leak from the engine. If it's hot outside and you're running the Air Conditioner (AC) and you back up and see a liquid on the ground, it's probably condensation from the AC unit. Or, it could be collant leaking from the engine. How old is the car? Do you consider radiator hoses to be part of the engine? Radiator hoses should be replaced every 3-5 years, especially if there are bulges, or if they're leaking.
it might be the intake gasket
your head might be going out
Back of the engine on the passenger side.
Could be a heater hose
I would suspect a leaking water pump, if I remember correctly it is mounted right in front of the timing cover and if it is leaking from the back the water will find it's way out somehow.