We run Penrite Manual Gear
Oil 75(was called Ultra Light) in the black Harrison. It has an old re-built Tremec 3550.
Oil gets changed 2 -3 times a year due to all the racing.
http://www.penrite.com.au/files/QW0B...GO7580-PIS.pdf
Have tried the equivalent Castrol product, but the box didn't like it much.