Yes, the oil seals wear out inside the valve cover and this causes the plug boots to get really oily until the boots pop up. Also, you may have a loose plug which is leaking compression in to the spark plug well and forcing the boot out. I would replace the valve cover gasket and plug seals with factory parts from the dealer. They are e more expensive but they work really, really great. The wires are most likely pretty oily so they need replacing as well. I would use NGK or dealer wires. If you don't replace the oily wires, there will be misfires as the spark jumps though the wet, oily boots.