I have a 2003 nissan altima and recently had the valve cover gasket changed and was told that I had to change the valve cover as well because the the seals in the valve cover where the spark plugs go are not replaceable so even if you change the valve cover gasket oil still gets thru the seals up top and on your plugs resulting in your car misfiring and smoking ...you can get the valve covers on ebay fairly cheap or there about $150-200 @ the dealership hope I helped you out some..