One of the reasons for erratic or failure of the angle drive is that there should be a substantial washer in the connection to the gear box. Otherwise
the short drive cable in the angle drive bottoms out in the gearbox drive, causing it to buckle. There was a BMC service note which I have a copy of but cant manage to post a copy here. If someone emails me at <b.caswell@virgin.net> I will attempt to send them a copy for posting here.
Ben