Egr cooler problem ????

Have a 2005 VN with D12 engine.Truck uses 2-3 gals coolant daily. No external leaks,no coolant in exhust pipe no white smoke out of stack while operating.Apprears there maybe oil in the resevior tank.Driver reports that truck will intermittenly loose power during the day.There is a lot of oil emmittening from the clamp in front of the reed valve which connects the air tube to the mixer box. I was thinking possibly a bad EGR cooler but the oil is throwing me off. ANY IDEAS. THANKS IN ADVANCE

 

Pablo how is the oil getting up into the reed valve ? From the oil cooler Thanks for the help