I was talking to the guys at Southern Gear, who rebuild nothing but manual trannies, diffs, and tcases, and they told me the same thing I heard 10 years ago about Mitsu 5spds. They recommend dexron atf in the tranny. The other guy had used it for over 200k miles on the original gearbox, and he didn't baby it - fast driving and heavy towing - and it shifted like butter, with no whines or grunches, and the shifter didn't move when you got on and off the gas (worn thrust washers or bearings).

Not responsible for advice not taken...