To your comfort, you're not the first one with an 1800ES who experience this. I have the same problem which at the moment prevents me from doing a long overdue MOT. I also suspected the right angle drive, and found that the shear pin was gone. Replaced it, only to see that it broke instantly again. It finally showed to be the speedo which had literally seized. Am now waiting for a workshop to return it after repairs ($$). To my experience, you have up to five possible culprits, of which the speedo or the angle drive are the most likely unless the wire cable has gone. If you find a broken shear pin, do not replace it before you have found the reason why. Otherwise have a nice and safe trip!