it's a manual cable in all mk1's
it's snaked from the gauges, through the front firewall, down through the front trunk (only a few inches can be seen in the frunk), down under the car, (between the plastic shroudings and the fuel tank), then into the engine bay from below, then comes up kind of along the exhaust manifold, then over the trans. Bolts into the top of the back of the transmission. A lot of the time the cable will not unthread from the drive gear... the drive gear is held in place by a flat piece of metal bolted down by a 12mm bolt. Unbolt the bolt, pull the flat piece of metal out, and (with cable attached is the easiest) pull the sending unit out. Unscrew the cable from the sending unit, being careful not to bend the casing of the threads on the cable side.
AFAIK, the at and mt have the same cable. The sending unit is "one piece", with a plastic gear. If the plastic gear is shot, then there's a chance the plastic receiving end in the transmission is shot too.
Hope you're a little more patient than 6 hours in the future for detailed answers...