So finally got around to this today - almost there but not quite 100% before it went dark!
I will write up when complete, but in short so far has been a new wheel, switch, slip ring and one additional wire
When done I adapted the new slip ring and then used the output tests to turn on the wheel - started to warm up nicely but then a symphony of warning bongs and the dash lit up like a Christmas tree - almost every module reported an error in VCDS!
After some troubleshooting I remembered my tendency to overlook the obvious, checked the fuse for the steering wheel module and it had popped - on checking it's a 5A fuse if you don't have a heated wheel and a 10A if you do - the heating element seems to draw about 7A
Changed that, set about clearing fault codes in every module - all back to normal again. Slight issue, I re-coded the steering wheel module for a heated wheel, but I can't switch it on using the button. I can see from the measuring blocks the button works but when I press it I get the message "Heated Steering Wheel Turned Off" - it should toggle on then off.
I suspect a minor coding issue - but it is dark so gave up - maybe tomorrow