Both bushings and needle bearings, when new, work just fine. As in all things mechanical, when (not if) the pilot device fails, the damage done afterwards is the real problem. A failed bushing simply rounds out gradually, allowing the clutch input shaft to wander and eventually to destroy its seal. In severe cases, the case is rounded out & must be scrapped. When a needle beaing fails, it often siezes onto the input shaft nose, and as its a press fit to the crankshaft, there's considerable force involved. The nose of the ZF input shaft can be severely damaged and if this happens, it must be repaired or replaced. Repairing heat-treated gezr-grade steel is not simple and at least requires complete disassembly of the transaxle while being fixed. Tear-downs run in excess of $1000, parts extra. Some ZFs cannot be fixed; more 15 yrs ago, the replacement cost of an input shaft was $2600... for a good used one. So I use & recommend softer bronze pilot bushings that do no damage when they go south, and I keep track of my clutch action so I have some warning when things are not happy down there. Incidently, when iron-contaminated bronze (magnetic) bushings lose their oil supply, they gall and abrade input shafts almost as well as a siezed bearing, and the required repairs are identical. So, there is no known performance advantage to using a bearing or a magnetic bushing, but considerable ri$k. Your choice....
