Ducati SCRAMBLER 800 Workshop Manual page 838

Note
When refitting used components, before installing the gearbox assembly in the crankcase half, make sure
that the inner races of the gearbox shaft end bearings are fitted into the correct bearings and have not been
left on the shafts.
Match gearbox shafts, fit the calculated shims and fit them to the clutch-side crankcase half.