DD15 oil leak and in reservoir

you need to make sure you have oil or diesel in reservoir. if its diesel then you have bad o rings on injector cups. if its oil then could be many things

 

no egr cooler is not oil cooler. the oil cooler element is located inside of oil cooling module. what year is your dd15?

here is that cooler

 

Have the same problem took it to the shop almost 7000 to fix it

 

why $7000? do you have printed estimate?

 

I just had the gaskets changed on my oil cooling module, but it was just an external leak. Nothing was in my coolant.
The crankcase breather was also done for the same reasons. But that's something you could do yourself.

 

Some drivers can change it for sure , its easy .

 

Here's the proceedure to remove and install the oil coolant module.
https://ddcsn-ddc.freightliner.com/cps/rde/xbcr/ddcsn/605-15.pdf