What is involved in a master cam replacement on 2003 Nissan Sentra

Mechanic told me that there was coolant mixing with oil and my spark plugs were wet.
The car would not start (would turn over), loosing coolant without an apparent leak and the temp would go high then low, loss of power,

Asked by for the 2003 Nissan Sentra
sounds like a blown headgasket to me.not sure what you mean by master cam repl