How did you fix your valve cover leak?

One good solution taught to me by an old mechanic was to check the obvious, of course, make sure the valve cover flange and holes are nice and true. Clean and tap/clean the bolt holes in the cylinder head. Make sure all sealing surfaces are clean of grease and oil and free of old sealing materials. Then when you are ready for the install, using engine paint in a can, spray both sides of the cork gasket with a film of paint. The paint seals to all the mating surfaces and helps prevent leaks. This has worked for me.
Just make sure to paint the cork side that mates to the valve cover first and affix it to the VC. Then paint the side that mates to the cylinder head. Not alot of paint, just enough for a film thats sticky as you are putting it together.