2000 Century oil in cooling system?????

Question for the AF Techno-heads:
I had my 2000 Century in for regular service and the shop called to tell me that they found evidence of engine oil in the cooling system. A couple of months ago they showed me a small leak where coolant was seeping from the intake manifold-to-head interface. At the time, the shop said its a minor leak and just to watch the coolant level till it gets worse. Also this is a common problem in this engine type (3.1L). I checked it again myself recently and it appeared to have stopped. But now its worse I guess but I can't understand why there would be oil in the coolant. The coolant passes from the heads to the manifold and back so the leak seems to be most possible from the manifold/head gasket sealing the coolant passage. The coolant prressure would seem to always to be equal or higher than the area beneath the manifold. I can understand coolant in the oil, and I've actually experienced that from a V6 intake manifold leak on another car. But there would have to be presurized oil someplace leaking into the coolant for this to happen.
Any ideas? :1zhelp:

The oil pressure(40 psi) is much higher than any pressure in the cooling system (18 psi max). Especially when the engine is cold. When the engine is cold you have no pressure in the cooling system. You will need to replace the head gasket. When putting everything back together you may want to use regular (green) antifreeze, not dexcool. The dexcool antifreeze will gel if exposed to air while hot (contains stop leak). When the first leak developed the level dropped exposing the coolant to air. The gel can obstruct small (eventually all) coolant passages. The resulting pressure came exceed what the system can handle, so you blow a head gasket. Go to Google and do a search on Dexcool problems. You will get THOUSANDS of hits. There is a group tring to get a class action against GM for these issues. Also some people have gotten GM to pay for repairs. The repair most often found is exactly what you describe. I have a 1998 Century 3.1 V6 I found a little of the gel on my radiator cap and found all this info when looking for an answer. I flushed out all the dexcool (don't forget the overflow tank and hose) and replaced it with green. I have no more trouble. I hope this helps. Good Luck.

intake manifold gasket leak