Mike/Michael – you are right!

Mike – I'm sorry I misunderstood your first reply – your interpretation of my pics was right on the money. I feel foolish now – after having come to the conclusion that the pinion must be keyed to the shaft I should have realised that the keyway has to extend to the end of the shaft – the boss visible at the botton of the above is welded in place, so no way was it coming out in that direction
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It was actually worth pursuing the strip-down this far – the shaft is bored to allow lubricant to pass to both bearings, and it was pretty much caked up.
So another result – thanks!
Robin