Gents,

This is the 2 hoses I speak of : Hose 1 is item #180 and Hose 2 is item #150, for typical W212 gasoline engine.
The coolant flow as follows : Engine block >>>Plastic pipe #1 >>Plastic Pipe #2 >>> Hose #1>>>Hose #2 >>>Heater core IN>>>Heater Core OUT>>>Return hose #250




The plastic Pipe #1 for M276.9 engine, you probably will never find it....LOL.
It is located in EPC under Exhaust Gas Recirculation....crazy !!!!! I guess the data entry guy was doing his job after the long OctoberFest , the Beer Party in Germany





.
At the least for my M276.8 engine , pipe #1 is where it is supposed to be, under ENGINE COOLING





.
I just found an example of the Hose 1 and Hose 2 failure mode. Its the plastic always or the internal o-ring.
The rubber hose itself is good. I cut already 2 of coolant hoses from my car so I can study them while I was trying to install in between the cuts, a coolant pressure sensor adapter.
I have cut Hose #1.

From a CLS500/550 of 2014.Mileage unknown. Engine is M278. This car has wiper fluid heater, the hose barb/nipple for it is the one which crack on Hose #2.
On his Hose #1 equivalent, the plastic end which is supposed to be smooth to seal against the o-ring on Hose #2 receiving end , have gone rough and that is small leak.
So basically Hose #1 and Hose #2 failed.

Below is Hose #2



.Below is Hose #2





.Below is Hose #2




Below is Hose #1




Hose #1 to Hose #2 mating region.




So those with heater option for windshield washer fluid, do take note that your plastic section of Hose #2 is weaker than non heater car.


=================

Since these are my 10th year limit components :
I will be ordering & replacing my Pipe 1, Pipe 2, Hose 1 ( stock in-hand ) , Hose 2 and Hose 250 ( HVAC Heater return ) and a lot more hoses.


So, older cars more than 10 years.....do take a closer look at this area yah.