If anyone is interested, I forwarded my engineers report to the supplying dealer, who pointed out that the car was outside warranty. So I sent the report to the distributor and hey presto. Courtesy car for a week. They are going to replace the entire gearbox (cheaper in man-hours than replacing "the two offending computers"), they will replace the steering box and power steering pump, service the car, valet it, for nothing. It's going in next week, and going for sale the week after that....