ColoEd,
My apologies I did not notice your message for so long, hopefully you've gotten your troubles taken care of already. In my case, they first replaced the oil cooler, thinking that maybe that was where the coolant was getting through. That didn't fix it. They then rebuilt the engine thinking maybe the head gaskets or something, that didn't fix it. Cummins finally agreed to replace the engine, and that fixed it. New engine has been great and no more trouble. Apparently the first engine had what they call a porous block, it had a leak somewhere in the block between the coolant space and the oil space. Good luck!
Thanks,
Alan

I just discovered oil in my coolant in 06, DSDP ISL400. Just wondering if yours was cured with the engine block replacement?