Spark plug tubes

Welcome to 2CarPros. There are replaceable seals at the top of each of the tubes if they are leaking. That is a common problem with them.
The tubes themselves are a press fit into the head, but they have a glue that bonds them in. It it possible to replace them but it isn't a fun job. You need to use a puller and heat them at the cylinder head to break the glue free, then pull them out. Then you clean up the left over glue and scuff the bores to be sure they are clean. Then you take the new tubes and mark them at 43mm. This is the install depth.
Now you pick one tube, apply the adhesive Three Bond 1324 or Loctite 271 and press it into place to the proper depth. The trick will be pressing it in straight without damaging the tube.