Eureka! I have totally re-formatted the machine and installed a fresh copy of X-Plane plus the Brunner software (plus the graphics, etc) – at super-slow download speeds, yet only an overnight job.
It works perfectly in 2-D.
I am now downloading the Oculus software to take it to 3-D.
I suspect, after around four years with the Brunner yoke, that one of the numerous automatic updates (Windows, graphics, etc) – plus FSX and other various installations – has created some sort of conflict, but will never know.
The good news is now – problem solved!
Huge Thanks to Stefan and his team and happy flying 🙂