I found two of this when I took off the value cover plus one in the oil pan awhile back. I can't figure where they came from...any idea

 

No mystery no more..... ferrule from the valve cover gasket. It's located in the gasket where the valve cover bolt passes through to the head. Used to prevent over-tightening the valve cover bolts and crushing the gasket which would cause it to leak.

Finding them where they're not supposed to be is common.......