manifold studs

The studs that turn in the head are definately not into a water jacket or wet hole. Those that are in a wet hole usually break :(
Spray some brand of penetrant on all of them and let it soak a day. Studs that get replaced in wet holes should get a little rtv silicone on the threads.
Note' teflon tape is reserved for tapered pipe threads . Bolt threads are not designed the same and tape shouldn't even fit between male and female .