1997 Taurus 3.0 "U" engine, 107,000 miles. Head Qu

I have found that I have coolant leaking into the oil. One mechanic has told me that the heads on my engine are cast iron, and he doesn't believe the problem to be there.

He does think that the intake manifold is either cracked or leaking at the gaskets. When I called the local auto parts store to price an intake check, the manager told me that they have not been seeing many intake problems with 97 taurus's. He did say that their experience shows that the heads themselves are being ruined when this engine overheats. He believes that I need new heads.

Any help would be greatly welcomed.