As mentioned above, I'd use new gaskets.
On mine I pre-fit the manifold and inspected all the mating surfaces as well as pre-fitting the gaskets for inspection.
For final installation I used a sealing product called "The Right Stuff" in areas where I found gaps that I didn't like the look of.
Then a light a coating of aviation gasket seal on all the metal to metal "meeting" surfaces that are gasket sealed.
Once the manifold was in place I made sure all the bolts had a good start to them and used a cross over sequence working back and forth from opposite ends, slowly and equally snugging down each bolt a few turns at a time.
Once the manifold was snugged up I torqued them down to spec. using the same sequence as described above.
