Muddy fluid in my coolant reservoir

[Dustito]

Hey guys I have a 2006 407 2.0 litre diesel. I recently noticed in my overflow reservoir is filled with a muddy looking fluid. I know this sounds like a major problem(like a cracked gasket). But theres no white stuff in the oil and as far as I know it's uncommon for diesels to have that issue. It's not over heating at all either...has anyone else had this problem or know what it could be?
Cheers

 

[dmccurtayne]

Heat exchanger it’s part of the oil filter housing


Garage C5 X7 3008 XTE
Gone but not forgotten 206 GTI 180 306 XR SED 405 MI16 x2 xzara VTS 406 SV 206 XT Berlingo 2011 (best car ever) 306 HDI 307 XSE HDI touring
Fix it right the first time

 

[Luke G]

I agree, I replaced an oil cooler on my 308 after a similar event. I bought the oil filter housing and cooler as one unit off eBay. It was new and about $225 delivered from Germany. The cheapest I could get one in Australia was around $600. It’s a bit of a task to remove and replace the housing due to
difficultly of access but certainly not impossible. Once done I flushed the cooling system 6 or 7 times, I still get a bit of oil in the coolant (not much).