valve covers that won't leak - ??

I have mopar performance covers with the thickest fel pro cork and metal gaskets you can get 5/16 I think forget the number of them..After you snug them down and start it. The next day go back and snug them up again.The cork compresses and you have to re-tighten them and couple of different times. I found out after I did this that the bolts where to long after the gaskets had compressed and they bottomed out making you think they where tight. Have not had a problem since I put in shorter bolts. Actually had them off a few times with no leaks