Outer Limits 4x4 Board

G'day, as my topic says, I'd like to find out what is actually involved in a Diesel Injector service? My 1990 Paj hasn't had new injectors fitted since 2006. People say that you should replace your injectors every 100,000km (mine have done much more than that). I've heard people on this forum mention that you are looking at approximately $450 for a 4cyl diesel injector service. Does this involve the person removing the injectors and refitting new ones, or is there something more to it? Thanks for any advice, Sam.