The drive-shaft boot and the seal inside the boot, can be replaced WITHOUT removing the gearbox. The car needs to be on a ramp, or up fairly high on stands (NEVER work under a car on just a jack).The drive-shaft is disconnected at the coupling end (4 x 13mm bolts), the slider on the shaft slid back, the little 'stop' ring on the end of the drive-shaft removed and then the slider slid off the shaft. The boot is removed by undoing the 4 x 10mm bolts that hold the boot's securing ring--the boot can then be slid along and off the drive-shaft. Note, there is a metal ring that will come off with the boot--this is the 'locking-ring' for the adjuster ring of the diff bearing on that side and must go back on when replacing the boot. It will probably only go back on in 1 specific position on the adjuster ring of the bearings. Inside the boot there is a holder for the seal---ease that out and replace the seal. When fitting the seal holder back in, it helps if you lubricate the holder with some rubber grease. Refitting the boot is basically the reverse of removing it--don't forget to refit the 'locking-ring' and the 'stop' ring on the end of the drive-shaft as well as the spring that goes in the end of the drive -shaft and sits up against the alloy/rubber coupling. It is a bit of a 'faff' rjob, but not difficult. I have seen a 'u-tube'film showing this job--it was on an 'Autobianchi', but the engine and gearbox is exactly the same as a 500.
