Quicksilver...
I use the "Full Synthetic" Quicksilver brand of oil and have been for about 4 years.  It meets all of BRP's requirements for use in Rotax engines and states so on the back label.  They also make a synthetic blend.  
When I was looking for an oil, the closest BRP dealer was about two and a half hours away.  That's when I went on a search for another oil.  I found the Quicksilver near me and a really good price.  It's stocked at my local Walmart store, just down the road......:cheers: