On a 2nd timing belt change I replaced my pump because it felt slightly but unimstakeably loose and had more friction than a new one when rotated by hand. It was not leaking. If you, like me, drive moderate to long distances, to sometimes unfamiliar places, why risk a failure when and where it might be hard or expensive to do anything about it? That said, I would not personally have replaced my pump if it was truly symptom-free. A dealer tech gave me the same advice.

When replacing the pump, remove the tensioner assembly, then the pump. Then replace the pump first. It would be hard to maneuver the pump in with the tensioner assy in place.

My dealer-supplied pump came with new mounting bolts which were pretreated with some kind of sealant or antiseize substance. The gasket was dry and I used no sealer on it. It does not leak so far (about 6 months). I would inspect the sealing surface under a bright light to be sure it is very clean of old gasket and debris.