piston ring leaking

Hello,
As a general rule, oil on spark plugs can be caused by bad valve cover gaskets, worn spark plug o-rings or valve guides, a faulty head gasket or a broken piston ring. Symptoms of oil on spark plugs include blue smoke from the exhaust, poor fuel economy and engine misfires.
The leaky valve cover is more common reason for oil in the plugs.

Here is a helpful video:

https://youtu.be/9M6xWMMRe0E

You also might find this article helpful:

https://www.2carpros.com/articles/how-to-change-spark-plugs

Thank you.