Cant remember the DT but normally the way is to look into where the speedo cable goes and there may be a couple of slots showing. This allows you to unscrew this holed, circular, bolt out and then the worm drive can come out. The TS looked worn and I managed to find a NOS one off US fleabay. The old one still works fine so I have kept the new one for when I do need it. They can be brass so softer than steel and here may be a little rubber washer in there.