A. Yamaha recommends
an "all weather" gear oil weight of SAE 80W/90, GL4. For specific temp
riding, they recommend; Above 40° SAE 90, GL4 and Below 40° SAE 80, GL4
Comments: I use Valvoline® Brand high-performance gear oil in both of my Viragos and in all 3 of my cages. I've never had a problem, and it's relatively inexpensive.
For the chain drive models of the Virago (XV920RH) Yamaha recommends Shell
Advance 1 (now called Shell Advance Ultra Chain)
or lithium-base EP2 grease.