Help w/oil in water

Been lurking in for awhile now. Great forum
Have a question. 1996 Lumina w/3.1 It has oil in the water, an oily residue in the neck of the radiator, no visable external leaks & runs great.Intake or head gasket? Mechanic say head gasket but he did not perform a leak test. Said a compression test was inconclusive. Any tests I should try?
Thanks in advance

If there was no overheating episode preceding the problem, the logical assumption would be the intake, a common problem with the 3.1.

Oil in the radiator could be more trans fluid than oil. It could also be lack of coolant care. The intake manifold gives alot of problems but never seen it to get oil in water. Thoses cases you are dealing with a intake gasket and no oil pressure there. In cases of that water leaks and drains down into oil pan.

99% it's an intake problem like jeff said

99% right,bad intake gaskets.I have replaced two or three or 3.1s because someone drove them with bad intake gaskets.The oil had to be drained out overnight(the engine oil was like mud).