So to round this one out - after I kicked off, amazingly the part they were waiting for arrived the next day and was fitted Friday afternoon.
Picked the car up last Saturday morning and it finally seems to be all working great. All modules updated and R59 installed. Already up to 800 miles (had 330 on it when we collected on Saturday). Even the vibrations aren't as bad as I remember.
Back in love with it (assuming it carries on working for a bit longer at least

)
Quick question - car doesn't seem to have been supplied with a granny charger (no big problem as have a wall box at home). Did the granny charger come as standard with the car? Dealer haven't responded when I asked for one to be supplied. TIA