If you have the plastic upper intake that has never been replaced it could be leaking coolant from the EGR area into the oil, or from the lower intake gaskets into the oil, assuming this is a 3800 V6.
To test for coolant in the oil, check to see if you oil level is rising. Or, does it look kind of cloudy, or milky brown. You can also put a couple drops on a hot surface. If it only smokes, it's oil. If it sizzles, there is water present. You could also put the aforementioned dye in the coolant and look for dye in the oil. Or, it could be seeping through the head gasket and getting burned. If it's just a little, you may notice no symptoms. Does it run rough on startup and then smooth out after a few seconds? If yes, that could be coolant pooling in a cylinder and causing a misfire.