The shock mounts in the NB are made of solid steel, so they'll last the life of the car. The bushings that go on the shock shaft, however, should be replaced as they age. The rubber deteriorates over time. We recommend changing them whenever you change shocks. Unless you're the sort of person that changes shocks like some people change socks.
These new bushings are factory Mazda parts, but you'll find they're thicker than your old, worn ones. You may have to squeeze a bit to get everything assembled - that's how Mazda designed it.
This kit includes four upper and four lower bushings. That's enough for one car. Mazda part numbers are NC10-28-775 and NC10-28-776. Included in our NB shock conversion kit as well as the NA versions of our V-Maxx and Fox suspension.