The cam plug leak is uncommon. Probable cause is someone who changed cams and rammed the new cam in against the plug, disturbing it. It's a thin freeze-plug, installed backwards. All GMs and Fords use the same setup. Some guys coat the plug with RTV or Permatex 2 before gently tapping it in place (probably unnecessary). They're cheap & easy to install- I'd pop it out & replace it.
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