Volvo Penta gear oil

[DownWest]

A classic scandinavian double ended motor sailer fitted with a Vovo Penta B20B petrol engine and factory gear box. Does any body have any idea what oil to use? This is a question from my nieghbour who´s got some (fresh) water in the box and needs to change it.
Thanks in advance,
Andrew

 

[ccscott49]

More than likely the same oil as the engine, a good multigrade. But not sure.