Following on from this post I have had had my stub shaft and gear machined to correct asymmetrical wear on both the shaft and bearing resulting from a loose key in an incorrectly sized keyway. The wedging effect of the loose key resulted in an egg-shaped wear pattern on the bearing/cog fitting and an oval shaft.
This was rectified by boring out the bearing till true and cutting a correctly sized keyway. The stub shaft had to be replaced with a larger one to take up the slack.
The bearing/seal surface close to the flange upon which the gearbox oil seal acts was also resurfaced.
Below are pictures of the repaired assembly which cost around £600 in machining.