Re: Head Gasket - Oil Leak
Hate to be a smarty pants, but who ever said that the Expedition was a reliable vehicle?
Re: your oil leak. I'd get a second opinion. A leaking valve cover gasket is far more likely than a head gasket. Best way to diagnose this is to clean the engine, add a dye to the oil, drive if for a few days and then use a black light to see where the oil is coming from. Much better than guessing.