I was changing my spark plugs and one of the plugs I took out was covered with oil. What does that mean and what caused it?

 

If just the bottom of the plug was covered in oil, possibly blown rings, if the threads were also covered in oil, most likely bad spark plug tube seal, get a new valve cover gasket set with new spark plug tube seals and replace them.

 

well the problem is I just got the new valve cover gasket set with the spark plug tube seals like a few months ago. I don't think I need new ones already since it was like back in the summer of August IIRC.

Could this happen because of how it got installed?