75w80 synthetic.
The Fuchs sintofluid gear oil is quite good.
See below;
http://www.opieoils.co.uk/p-981-fuc...w-80-synthetic-manual-transmission-fluid.aspx
i use 75W90 semi in all of mine, works fine
I only use the Elf one: Elf TRANSELF NFJ 75W-80.