Regular hyd oil, like Shell “tellus” is a fairly low grade of oil, that is all gear or vane pump hyd systems require. Atf, motor oil , or hyd gear oil all work fine to, but are more expensive.
Atf is often spec'd because it flows good over a wide range of temperatures.
Your 1737 does not (?) have a hydrostatic drive, and if it uses no wet disc clutches that run in the hyd oil (some of the small bobcats used the hyd oil to also cool and lube the wet disc transmission clutches). If its just a basic hyd system gear pump valve and cylinder it likely does not matter what oil.
We switched out our clark skidders from atf to motor oil for a basic gear pump system and it runs cooler hyd temps, we were having trouble cooking cylinder packings, at motor oil drop the temps @ 20 degrees. But these machine work long 10 to 14 hour shifts and only in the summer months. So warm up time is not a concern. Motor oil has better lubrication properties then atf. Most skidsteers with hydro drive systems, require motor oil for the hydro, and because the hydraulics shares the same reservoir the use it to. This is likely why you have read about using motor oil around this forum.
However if atf is spec'd by Case and your not having ant trouble why change? If the oil in it is red, I'd stay with atf, it warms up easily.