Hi jasonj,
Yes rebuild is an option, the plan is to split the box to explore the extent of the damage once off. However I've just purchased the vehicle. A driveshaft seal is pouring oil out and i believe it has been driven around in it's current condition for a long time. With the noise it is making I'm not holding out much hope to it being salvageable.
I have not been able to find a NBX box for sale within the UK that isn't priced stupidly, so am looking to other options.
Many thanks,