I have had these leak before. On the back of the intake camshafts there is a VTC silinoid. This can sometimes leak, or it could be the valve cover itself. I would suggest getting Permatex Ultra Gray liquid gasket, two new moon seals, the two intake valve cover seals, and lower to upper plenuem gasket. It is not a hard job to do all of this in one shot. The Ultra Grey permatex is for the exhaust valve covers along with one half moon seal at back of each, and the VTC silinoids on the back of intake valve covers. then rubber gasket on intake valve covers, and finally the upper to lower plenuem gasket as you button up the motor.