Hoping I can get some guidance and/or confirmation on a problem I've discovered with the 2003 WG 2.7CRD, named by the kids as "Matilda". Seems Matilda is a bit sick. The coolant fluid level indicator had been coming on for a day or so, so yesterday afternoon I went to top it up and discovered oil in there. My first thought was "head gasket" which sent the moths in my wallet fluttering for cover. I did the obligatory online search for this issue and it seems there are 3 possible causes; 1 - head gasket, 2 - Oil Cooler, and 3 - Transmission cooler. After reading and watching some YouTube vids online I suspect one of those but will leave that until later to reveal.
Symptoms; Apart from the low fluid level, nothing has been out of the ordinary with the car. My wife drives it usually and so it was she who told me the "battery" light was coming on. I told her that was the fluid level light. It has once previously been low so I didn't think too much of it.
Oil Filler Cap - checked for milky white stuff, nothing, just black oil (see photo) Note oil change done about 3000km ago.
Dip Stick - Nothing unusual here it seems (see photo)
Fluid Filler Bottle - Oily substance looks black in colour, no red or other colours present (see photo showing paddle pop stick dunked into bottle)
Transmission Fluid - Opened the line that goes to the intercooler and drained a small amount - looks okay (see photo). Note it's on my to do list to change this and I have no history of when it was last done if at all.
So based on the above I'm leaning towards the oil cooler being the problem as there appears to be no evidence of coolant getting into the engine oil or transmission fluid. I'll admit I didn't even know such a thing existed so I'm learning on that one. I've not as yet downloaded a manual but did see in my searches that it appears an onerous process to replace it. Some of the YouTube videos make it look pretty straight forward but different vehicle makes. I've attached a photo of what could be the cooler and happy to be advised if that's correct or otherwise.
So based on the above I'm interested to hear if others think it's the cooler. Any other checks I can do? I can take the car to a mechanic to see if there are exhaust gases in the coolant but not keen to drive it too much. Thanks guys.