In the UK I use triple qx 5w40 fully synthetic car oil. If you look at the specs it's basically the highest spec car oil you'll get before they add friction modifiers. I can't find a direct replacement for rotella t6 sadly :(.

I think that the Shell Rotella is similar to Shell Helix. Beta riders in the USA use the Rotella T6 instead of the nasty pond water that Beta fill their gearboxes with at the factory. The Triple Qx is good stuff and I know a few people that use it with no problems in 2T boxes.

I go to a local bulk oil supplier and get UTTO (Universal Tractor Transmission Oil) for my older Yams. Never had a problem and it is about $90 AUD for a 20 litre drum.

Same spec as mineral trans oils, suitable for use in wet clutches.