Not necessarilly the case mate.
Ive recently bought a seal kit for the clutch slave cyclinder. I stripped the old one, cleaned thoroughly replaced the seals and boot etc and its better than ever. I personally dont see the point in scrapping a perfectly good housing made of cast iron in place of an over priced new item from Nissan.
As long as the unit isn't damaged, to me its the sensible thing to do. After all this is what all the old mechanics used to do, unfortunately today the so called mechanics are really just gloryfied fitters i.e. replace parts for new.
My own view and dont expect people to agree but rest assured the jobs i do, i do with 100% confidence and quality (blows own trumpet :lol
Ant.