replacement intake studs

Is it just the uppers that hit water and need to be sealed? I am going to be putting mine back together soon and most of my studs are still in the head and in good shape. I was thinking of pulling and re-sealing them, but did not want to mess with any that I don't have to. What is best thing to seal the threads with?

I used the dorman from o'reillys auto 89 cents a piece. be sure to use thread sealer on the upper studs they thread into the water jackets.