Greg, for the upper timing chain cover use a dab of MB sealant in each recess at the ends of the horseshoe gasket and a light coat of sealant on the mating surface of the timing chain cover to the head. It's important to carefully clean off all old sealant from the upper timing chain cover before reinstalling it ... making sure not to gouge/score the sealing surface. After I replaced the upper timing chain cover gasket there was no oil leakage.

No need for any sealant on the rubber valve cover gasket. Make sure the valve cover gasket is soft and pliable. If it's dried out or exhibiting cracks it would be a good idea to replace it.

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Fred Hoelzle