sorry ive been so slow, but I bought a s/h drive unit.
I have since fiddled with the broken pinion shaft, and
found that it was very easy to drill and tap the front end of the shaft. I placed the shaft in the lathe, holding it by the spigot inner race, and using a centre starting bit to create a starting point for a drill bit.
I drilled and tapped a 5/16 unf hole approx. 20mm. deep
using only a conventional drill and tap. There appears to be enough meat in the shaft to take the threaded hole possibly to 7/16 or 10mm. This fix is yet to be tried, but I think its worth a go, maybe by starting
with a 3/8 thread and a high grade capscrew.
If it breaks it is easily removed and taken up a size.
(the thrust bearing must be removed from the shaft,
it is in 3 pieces)
If you can do this exercise yourself, it is virtually cost free.