MOT Passed!
MOT time came around - the first in my ownership, always a bit of a stressful thought - but the car has passed with only one advisory for wear on one tyre shoulder.
In the same appointment I had the steering rack looked at for the 3rd time. I supplied a second hand rack from eBay and managed to convince the garage to have a go fitting it. I did not expect it to work, given the part numbers were non-identical, and fully expected to either have to send away my own (removed) motor for refurbishment, or to have to go to BMW and get the credit cards out.
I am pleased to say the mismatching part number replacement rack worked brilliantly (from a 2014 2.5, I think) and the car is now A1 again. A celebratory drive and wash today. Long live the Z4!!!
Retained the original rack and motor in case one day I do need to post it off for refurbishment and can avoid this absolute nightmare of a scenario recurring.
edit. 18th October
Just ticked over 1 year's ownership of the Z4 35i!
£1146 in fuel on 4170 miles, 28.8mpg, 348 miles/tank, 700L of fuel
£1100 of expenses; nearly all on the EPS problem in the end, although I did also replace ignition coils, sparks, and fit a cruise control system.
A total cost in the end of 52p/mile, or £2250/year, for year 1.