Now that I see the high resolution pictures, that is definitely the bypass check valve from the
oil pump. It looks like someone staked the plug with a chisel with such force that it split the plug. That weakens it to the point of being worthless. You will need to drop the pan and inspect the pump. You will see exactly where it came from and can replace the pump. This is the best picture I could find. The pump on the right shows the plug, while the one on the left features an adjustable valve.
http://rds.yahoo.com/_ylt=A0PDoX_J4d...2boil_pump.jpg