black oil on spark plugs any idea

[Peter0003]

Hi Everyone, Can you help? My K11 wouldn't start on saturday when I needed it the most. Later in the day I removed all the spark plugs & found they had black oil covering the spark area & threads how do I fix it and any idea how much to fix it?

Peter0003

 

[.Maarten]

Bad spark tube seals in the valve cover. You can replace those.