Hi Third Uncle,
That's pretty crazy bearing consumption.I guess that installation issues are out of the question along with Lubrication.
Have you considered Electrical Earthing.?
I'm just wondering if there is some low current circuit passing through the bearings. This will effectively cause Arcs across the faces & over time it will destroy the hardening.
It took me a change of Handlebars and 4 sets of bearings to find this issue on my 1150 GSA. The symptoms were similar and it was a nick in the loom on the Right hand side.............
Good luck & let us know how you get on.