Nothing personal. Just repeating what I read in the manual. When Polaris recommends the same thing under their brand name for both units and says "this is a substitute" for one of them, doesn't it stand to reason that it should be a substitute for both? Just looking at it logically... I might end up with the Polaris magic oil in the end, but I want to look at possible substitutes first.
When is a substitute not a substitute? polman is correct - 80W90 GL4 or GL5 is not a substitute for the transmission (chain case) - the heavier oil may cause problems down the road and the first problem will be trying to put it into gear at temps below 35 degrees F.
I use ATF TYPE F in my chain cases and two stroke motorcycle transmissions - Honda sells it as a 80/85W but it's about a 7W - all depends on who's scale you use. There is little uniformity in viscosity ratings between retailers
. Harley 60W motor oil was about the same as the 40W oil we used in our tractors on the farm. Today, Harley calls for 20W50 almost universally. I used to use nothing but Castrol 20W50 GTX in my 72 Triumph 650 - today, I use any brand of 10W40 JASO rated oil in that engine. The 71 and up engine had a self leveling primary and the same oil is used in the engine as in the primary. My CRF250 gets Honda two stroke transmission oil in the transmission/clutch reservoir and JASO 15W50 synthetic in the engine. I use JASO 10W40 in my lawn mower, snowblower, standby generators, pressure washer, 89 VT1100 Shadow and 99 Dodge Dakota RT because I buy it in 55 gal drums (cheaper that way) and I can go thru 55 gal in a year or two).
Sometimes it's just a personal preference - up to a point, any lubricant is better than no lubricant.
You can run an engine on Castor bean oil, soy bean oil, vegetable oil or glycerin oil (comes from animal fat), but at what speed and under what condition will it fail? Technically you can lubricate and engine with water, but it requires a very high pressure and certain metals will not hold up well (aluminum will lubricate better than steel with water and water is the lubricant of choice when working with glass).
It is best to use the recommended lubricant, but yes, there are substitutes - some may be better and some are inferior - how long do you want the piece of equipment to last and how much do you want to spend? Spend it on the lube or spend it on the repair - nothing runs for free.