Hi,
I like to soak the cork gasket in water for at least half an hour before installing, to help it form to the shape of the cover. Then I use a thin application of Hylomar on both surfaces. It's usually not possible to remove and reuse, but it also generally doesn't leak.
Someone named Justin used to make great silicon rubber gaskets for stock TR 4-cyl. valve covers. They cost more but seal great without any sort of sealant, plus can be used over and over. If you are interested, hopefully someone here can provide a means of getting in touch with Justin. I highly recommend his gaskets, but can't unfortunately haven't been able to use them on my car ever since I installed an aftermarket cast alloy valve cover. They only work with the original type of cover.
Cheers,
Alan