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. 

Additional Information: 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.