yeh, it has to do with resurfacing. cleaning out the bolt holes. new head bolts. run it untill it is warmed up. take the valve cover back off re torque the bolts.. 500 miles re torque the bolts.
I don't know how the factory makes them but this has worked for me.
maybe even at a 1000 retorque. I do it every time I have the valve cover off.