When a single part fails, other interacting parts are also likely to be worn or negatively affected. If only a single part is replaced, the next part is likely to fail as well before long, and you'll soon have to return to the shop.
By replacing the entire mechanism along with all the wear parts, you not only avoid more shop time with associated disassembly and reassembly of the mechanism, but you also get the latest versions of all original parts. It is simply the surest way to increase service life and reduce downtime.
You can save even more time by using the VBG service tool. With this tool, you can change bushings quickly and easily without having to heat or knock out the old ones.