Like Pete says ...... glue/seal your gaskets to the valve cover side only. Never overtighten the hold down bolts/nuts. 20-25 LBS max. It helps to be sure the valve cover mount flange is clean and flat.
What! I was just looking in the manual yesterday, for mine, and the torque value is 40 in/lbs.
I should have specified ft lbs ..... 20-25 ft lbs transulates pretty close to 40 in lbs.