Powersports/motorcycles have similar gear oil requirements and the industry is a good source for trans oils. They are non synchronized (no brass, dog gear synced), have a bevel (straight cut as well) gear primary drive similar to a ring and pinion. And depending on which oil, designed for wet multi plate clutch packs.
I have been using Bel Ray gear saver motorcycle oil in my 915. GL-5, non synthetic, 80w90. Not for wet clutch.
https://www.belray.com/product/gear-saver-hypoid-gear-oil/
Easily available from any motorcycle shop and usually on the shelf, but here is a link to amazon for easy lookup.
https://a.co/d/4dE95bb
These non synthetic options I have not tried personally but would be options for LSD 915s.
80w85 Thumper trans oil that is designed for competition dirtbikes with wet multiplate clutches.
https://www.belray.com/product/thumper-gear-saver-transmission-oil/
And they also have a trans oil that is straight 85w (listed on SDS) called Sport transmission fluid that is also designed for wet multiplate clutches.
https://www.belray.com/product/sport-transmission-fluid/
All of these oils are designed for extreme shock and gear load.
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