I was hoping if they hit the intake like mine did he would notice that pretty easy, and he doesn't have a leak on that side so probably not the issue.
Cork haskets won't do it, been there
Gluing them won't
Tightening the hell out of them won't
Making sure they are flat won't
The problem on factory style heads is that the rail has an approximate 1/8 arch to it front to back and the cover is straight. (without the gasket set it on and push down on the back of the cover) the front pops up about 1/4 or more.
Same if you push down on the front (the back pops up 1/4 inch) and it's not warped valve covers.
I did mine exactly the same as Swifter is doing and mine are dry as a bone in the the AZ desert, but if I tell how I did it in a public post there will be a shitstorm of posts saying how stupid my solution was, how it couldn't possibly work, or that I should spend a bunch of money on machining so I can run Fabbed covers on stock heads that I don't even need. (I have stock heads and valvetrain) and I did it for the look and possibly needing them on a different motor because I got a GREAT deal on them.
This was before I put the headers on about 8 months ago, and they are still bone dry, so it can be done.
As long as you accept and deal with the arch of the valve cover surface on the factory head.