allways put a small bead of sealent on em
Personally, I would suggest the opposite. The gasket *is* the 'sealant'. You would normally expect to use sealant or a gasket, not both. Many new vehicles use sealant instead of gaskets because of cheaper manufacturing costs.
The only time I would recommend using sealant on a gasket is if the surface is so badly pitted that the gasket cannot take up the irregularities. Or if the manufacturer specifies it. They don't for the 2.5 rocker cover.
Using sealant on the gasket just makes your life more difficult the next time you have to remove it!
The major cause of oil leaks in these areas, like the rocker cover, is over tightening the nuts. Cork gaskets are quite critical on being compressed correctly.