what are causes of an internal engine coolant leak

GMC SIERRA
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LOVETORQUE
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1999 GMC Sierra, K10753, 5.3L V8, auto trans, 104k miles, regular 4500 to 5000 mile oil changes with Mobil 1 5W-30, very minimal towing hauling of any weight. Used oil analysis says high Potassium (161) and Sodium (32) means coolant contamination.
Found Tech Service Bulletin, 06-06-01-019B, on bad heads that have porosity / cracking in area of oil drain "bowls". I am going to take valve cover off to inspect for this bad cyl head issue.
What other causes of coolant leaking down into the crankcase should I be considering, besides bad head gaskets? Thanks a bunch.
Oct 26, 2007 at 3:48 PM
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RASMATAZ
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Could be crack head and block-an intake manifold gasket between the head and manifold.
Oct 26, 2007 at 4:09 PM