Oil pooling

With regular gaskets, use Gaskacinch to glue them to the covers. That's all you should ever need for "sealant". No grease, no silicone, nothing else. But I found that the only valve cover gaskets that work 100% of the time are the Moroso "Perm-Align". If those heads use the stock "LA" style valve covers you need Moroso #93050. The gaskets RustyRatRod specified look similar to these Morosos.

Also, check to make sure that the flange of the valve cover isn't getting hung up on the intake manifold somewhere. A lot of aftermarket intakes do not play well with many types of valve covers. Usually grinding off the offending part of the valve cover, without destroying it's sealing ability, is the only solution.