Here's another spark plug story.

My chain saw had trouble starting and running. I did everything I thought to fix it. I had pulled the plug and inspection showed it to be ok. Well I had the plug out again and almost accidently turned it so the tip was facing down. As I did that I noticed the ceramic below the center electrode slipped down the electrode and closed the plug gap. When I turned the plug tip end up the ceramic slid back to the proper position. Replaced the plug, worked fine.

92 Montero LS 3.0L V6 Auto, Stock, Original owner, 185,800K miles