I usually back up paper gaskets with Permatex Aviation Form-a Gasket. As a bonus, it holds them in place during assembly.

For cork gaskets, I apply the Aviation stuff just to the pan side to hold it in place, and make up for any 'wavyness' or piting, particularly for steel pans. Also holds gasket in place. The block side is usually very flat, and if I have to remove the pan again, I want the gasket to mostly stay with the pan for easier cleanup instead of 'splitting' and making a mess.

For rubber gaskets, I would not use any goop unless the mating surface had pitting or was otherwise not flat. I would use RTV Gasket Maker to back it up, if needed.

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1986 300E 5-Speed 240k mi.