I had the same problem, fought it a few times. I solved it by cleaning both surfaces well. Put a decent bead of RTV (I used blue) on the valve cover side. Let it sit for 8-10 minutes. Then put it on the head. I tightened everything just enough (nutdriver) to "flatten" the RTV a little. Then, after it set over-night, I tightened the bolts up with a ratchet. Make sure you bounce around and do it evenly. I still didn't go too tight, just enough to press on the "flat bead" of RTV. I think the trick was to let it set up into the "thicker" bead then tighten down into it. It may have not been the correct way, but it solved my problem. Later, Brad