Bought this because my spark plugs had oil on them so thought I might replace them after replacing the rocker cover gasket and spark plug gaskets. Oil WILL cause the rubber inside to slip out of the socket and you need to be strategic when you know your spark plugs have oil on them. I've found that cleaning after each use reduces the chance of the rubber inside coming loose. Overall this is a good selling point and I wouldn't put you off buying it. Just be careful if you find yourself in my special situation! :)