hey, it is the spark plug tube seals more than likely. this engine unlike others can't be serviced. no way of just replacing O-rings. after the 100k mile run gaskets begin to show signs of wear. For this engine you need to replace the valve cover itself. replace this before it does any worse damage to your engine. the valve cover is 130 at oreillys and autozone. the oem spark plugs are 9 each. replace your valve cover gasket the felpro brand runs about 12 to 15 dollars depending your area. goodluck.