Oil leaking into the spark plug wells is a sign of a fairly serious problem that should be inspected and worked on immediately. It is almost always due to a failing gasket or O-ring but can also be because of a failing piston or worn valve guides.
Oil making its way into the spark plug wells will greatly affect the engines operations, leading to misfires, increased oil consumption and blue exhaust. In extreme situations, it can even lead to an engine fire. If the car is exhibiting any of these signs, the spark plugs should be inspected immediately.
How this system operates:
This issue involves two systems, the spark plugs and the engine lubrication system.
The main duty of a spark plug is to ignite the fuel/air mixture in the combustion chamber. Electrical energy is transmitted via the spark plug where it jumps the gap and the spark ignites the gasoline and air mixture. Spark plugs also draw heat out of the combustion chamber, working as a heat exchanger; it pulls thermal energy from the combustion chamber and sends it to the cooling system.
Engine oil is used to lubricate the moving componentst of an engine. The constant moving of the engine parts creates heat, as well as wear and tear. Engine oil helps to minimize the friction and dissipates the heat caused by the engine.
The oil pan is where engine oil is saved. A typical oil pan will hold up to 6 quarts of oil. When the engine starts, the oil pump pulls oil from the oil pan through a part called the pickup tube. The oil then goes to the oil filter, which removes dirt and debris before it is sent to the various components of the engine through spurt holes. Eventually it heads back to the oil pan to start the process over again