I use Polaris "SCL" (Synthetic Chaincase Lube) for all my Polaris and Ski-doo sleds. One bottle will do at least 4 sleds, all with reverse cahin cases. I buy it for about $12 a bottle, so that makes it about $3/sled. Why risk using other oils when its only a couple bucks per sled for something developed specifically for snowmobiles?
In the past I used AMSOIL, it was good but expensive, have used Polaris SCL for several years and have great results. Our "extra/spare" sled that only gets about 500 miles on it every year the oil looks like new at the end of the year and I will get 2 years out of it.
I am sure other oils work just as good, just my $.02