The pattern should be from the center out...including the screws over the plug holes...but from the center out...and it sounds like you're going diagonally across from back to front and front to back.
There must the be prescribed pattern in spaghettidecoder.org I'm sure...if not, I'll see if Bentley has it.
Make sure you don't have any residue of rtv from before...or anything stuck up in valve cover...though based on how new it is...me? I'd just loosen them up a bit and try a different pattern. If you do take cover off again, though, check the head and moons for rtv residue and clean it up well.
...and Bentley says in one reference, 18 ft-lb for vc screws, but recall seeing it listed as less than that elsewhere.
...anyway...good luck...let us know what it turns out to be...and try just working on tightening from the inside center out slowly...like an exploding firework!
Last edited by dmax; 07-22-2012 at 03:10 PM.