HELP!!Speedo not working... New gearbox reqd??

Hi there, My Golf Cabby's speedo has stopped working, along with the VDU etc. Now, thought it may have been the cable, but no. On closer inspection the "innerard" workings inside the gear box have dissapeared! I have been told that this is a common fault   (?) with Mk1 and " golfs, and I need a new gear box, as this cannot be repaired. Is this so? any help or advise greatly recieved! thank you :?