I recently changed the water pump shaft seals without renewing the shaft. To do this I first had to remove the impellor by punching out the roll pin. 1000 miles later both plastic pinions on the drive gear failed and it's obvious they were damaged when I hammered out the pin. So the moral is don't attempt short cuts, remove the clutch casing to change both seals and shaft. By the way the job is made much easier if you have replaced the rigid oil return pipe with a flexible hose.
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