1999 3.8L Head Gasket symptoms but Gasket looks fine

So I had coolant mixing with exhaust AND coolant mixing with oil. Radiator was loosing pressure under test and the infamous white smoke was near suffocating. Tore it all apart, and the gasket shows no signs of being blown or cracked. The machinist looked at the heads, and they were flat as can be. Nothing wrong with the valve seals and the block shows no signs of being cracked. Could it just be a fluke? Could the gasket actually have gone bad without physically showing it? or could it be something with the lower intake ( I highly doubt it though)?
 
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Based upon what you are saying it seems more likely the problem is in the intake. However it would seem wise to me to double check all of your "assumptions". Not knowing why it failed raises the chances of performing a major motor repair only to end up with the same problem. Almost everyone would agree that would suck.

i just don't buy that a head gasket can leak without showing signs of the physical damage path. If it is leaking from the head gasket then:
  • the damage has been over looked.
  • the heads or the block are not flat
  • the surface finish of the heads or block is not within spec.
  • not enough clamping force (problem with the head bolts).
Have the heads been pressure tested?

Has the block been checked for cracks beyond a visual inspection?