When I first learned that the Duramax was equipped with a gear driven water pump about 6 years ago, I thought about a potential for coolant in oil.

I have heard of a couple instances of water pump seal failure and coolant in oil. For example, the editor of Diesel World magazine lost the engine in his 2002 Chevy because of this.

I'd do what Mark suggested, then make certain coolant wasn't getting in the oil. I also might be inclined to replace the coolant surge tank cap if you discover a leaky water pump seal. Too much pressure will increase wear on the WP seal.

Jim