How do you tell if the valve cover gasket is leaking?

How do you tell if the valve cover gasket is leaking?
Its hard to really call it "leaking" You will generally start to notice a slow seepage around the valve cover, more commonly in the corners if not circling the entire valve cover. Replacing the valve cover gasket is cheap and fast, and can generally be done for under $75 including labor. ( prices can be higher or lower, generally not over $100 unless Lexus or Cadillac. )