318 valve cover leak

The drivers side valve cover leaks. I have pulled it and replaced gaskets 3 times...and it still leaks out of the back corner. I have even tried a new valve cover to no avail. I am stumped. I've tried cork and the new composite that is a little stiffer. I even went as far as using silicone between the gasket and the head. And I know the head surface is clean.
Any ideas?

You sure it's the valve cover and not the oil sending unit or intake manifold?

Did you flatten the hole and use the spreader? Is that bolt too long, by even an eighth?

these always worked for me on OEM covers
http://www.ebay.com/itm/Mopar-small-block-Valve-Cover-Gaskets-Rubber-OEM-design-273-318-340-360-/331770099992?hash=item4d3f09f918:g:CKcAAOSwvUlWszPx&vxp=mtr
I had a v/c leak problem before too. If silicone sealer has been used in the past, check the bolt holes for excess dried silicone. I use a pic to get it out of the hole. It keep the bolt from going down enough to get the cover snug.

Cast covers, blue moroso gaskets (there still garbage BTW) and RTV to seal both sides of the gasket was the ONLY 'fix' for mine.

Try a set of Mr Gasket ultras.If they dont seal something is bent or warped.My buddy just had a set or the high buck blues leak.Replaced them with the Ultras and no leaks.Silicone and cork dont mix.If you need to use both you have a problem.Rocky

I have fabricated valve covers, but I had the same... leak at the back of the drivers side valve cover. I found the valve cover was a little larger and when tightened down would twist the gasket down around the outside. I made the bolt holes slightly oblong on the valve cover to pull it ahead slightly. Haven't had a leak since. If you have an extra cylinder head lying around, maybe try the valve cover and gasket on it to get a good look on how everything is sitting on the head?

I don't usually recommenced the use of silly-cone.
However to verify it is the valve cover gasket, get both the mating surfaces super clean, don't even need to be completely flat.
Put a 1/4 inch bead of the silly stuff all the way around on the head.
Let it set up for a good 15 minutes.
Put the cover on and lightly tighten the bolts till the silly cone just peaks out from the edge and let it set overnight.
Once the silly stuff cures, it should not leak.
If it does, then as mentioned above, it's elsewhere.