E30 Zone

I have been wanting to change the oil in the gear box for a while but can't get an answer of which type should be put in. Some people tell me ATF fluid others say normal gearbox oil hypoid 80, I have been told it may need long life oil. Been under the car there is no (colour) tag. The number on the box is 033694 BCO. Can any one shed some light on this for me please?

SAE80 but if the car has a notchy gear change when cold use ATF.

Thank you for this info mate. The BMW dealers did not offer much help to this question.