If it turns out to be a leak in the Charge Air Cooler, I think GripGrip had an extra CAC he was wanting to unload, if he still has it. Here is a pic. of IM I bought from someone who had an obvious leak. Yuck!!
I don't know that anybody knows how long it took to actually get this bad. It could have been thousands of miles, so I wouldn't completely rule out the CAC just yet. If I had a leak though, I'd rather it be the CAC than a head gasket. It would also be a good opportunity to get it thermal coated. Good luck, I hope it's just a simple leak somewhere that was overlooked.