Assembly Guide has: ... Lubricate the plastic speedometer drive with gearbox oil and fit into the rear left of the tailshaft housing, Fig 1 refers, such that the speedo spindle locates in the orifice. Ensure the surface of the speedo drive housing is free from oil and apply a thin coat of silicon sealant. Tap the speedo drive housing cover gently into place. Lubricate the small oil seal with gearbox oil and slide down over the speedo drive output shaft. Gently tap into place using a suitable sized socket as a drift. The brass 'top hat' should be located over the oil seal and held in place by the circlip, Fig 2 refers. Ensure that the circlip is fully located into the groove as access is restricted when the gearbox is in the car. Do not fit the sensor. ... Screw the speed sensor onto the 'top hat' ensuring that the drive cable slots into the speedo gear output shaft. Connect the sensor to the two pin plug in the vehicle wiring loom. Fit the grommet to the RH side of the tunnel from inside the cockpit. ... Which doesn't seem to help much. Can you grip the thread on B to get it started and on as far as possible, then press and angle either inwards or outwards to seize B on C as you finish it? Or use some sealant, as Ian did? Jonathan PS: I've (obviously) never done this. Mine is fully mechanical. But I'd describe yours as electronic from the gearbox. PPS: Nice diagram.