Any further developments on your speedo issue?
I took a look at my gearbox yesterday. There are 3 connections. I guess one pair is the output shaft speed. Another pair is to do with the GAGS(computer aided gear selection), not sure what the 3rd does without looking I the manual. So currently not totally sure which connector it is, maybe worth cleaning up any contacts.
I did diasble the GAGS on one of your dads cars in the past by reprogramming the ECU.