Why is one spark plug covered in oil on your 1991 Geo Storm GSI?

A spark plug covered in oil on your 1991 Geo Storm GSI typically indicates an oil leak in the engine, possibly due to worn valve guide seals or piston rings. This allows oil to seep into the combustion chamber, leading to fouling of the spark plug. It can also cause poor engine performance, increased emissions, and potential long-term damage if not addressed. Regular maintenance and inspection can help identify and rectify the underlying issue.