Acually, if using synthetic gear lube, it shold be be 75-140w variety, NOT the 80w nor the 75-90w conventionable gear lube viscosity. As a synthetic lube of the lesser viscosity doesn't have near the 'cushion' needed for ring/pinion gears nor bearings.1st stuff that came out smelled like old fish on my ST1100 and Chris's ST1300.
I replaced with synthetic 75-90wt gear oil.
Mark