this is also a problem in Chrysler's old 2.0L SOHC "Neon" engine, except in that case, it had Separate Spark Plug Tube Seals pressed into the valve Cover. Over time, the seals would get hard and brittle, allowing oil to get past the seals, run down inside the spark Plug tubes, eventually submerging the spark plug and spark plug wire boot in oil, shorting them out against the Cylinder head.