oil in coolant overflow

My friend owns a 2004 Grand Prix with a 3.8 motor. He is noticing the brownish foamy kind of residue in his coolant recovery tank - which we think is probably oil. Do these motors still have intake manifold problems like the older 3.8s?

Do you think the intake gaskets is the place to start? Possible cylinder headgaskets? Possible trans cooler?

I was kind of under the impression that GM may have solved the intake problem. Thanks in advance!

How old is the Dex-cool or has it ever been replaced? Still 5 years or 150K miles, whichever comes first on replacement interval.

If this is the NA SIII 3800 engine then the UIM problem should have been resolved. It is a metal UIM plenum now. I've seen anecdotal data on the NET concerning LIM gaskets on the '04 and up so it is a possibility. Dexcool sludge is still not uncommon in the coolant reservoir.

BTW - How does the radiator filler neck look?

Yes, the question is with the radiator filler neck. My '99 GTP started to produce more and more brown sludge up in the neck, and after a LIM gasket replacement, the filler neck is nice and clean.
The sludge also collected in the Low Coolant sensor, causing that to provide false low coolant light ON.