USED-Thrust block in the differential between the planet gears was left out on the turbo models and others at same time but reinstated again a few years later. IF you have lost yours these are available as USED only, but the diff pin is fairly loose in them as standard because they get covered in oil. Very rarely were they changed for wear as the output shafts were apparently centrifugally pushed outward.
original cost new was about £16-00