I have read that in a 743 you can replace use 1040 oil for hydraulic fluid. I doubt I can find Mobile Hydraulic fluid around here.
The real old machines used oils like 10W-40W. Then in later models the manuals only recommended it if the oil was low and you didn't have access to hydraulic/hydrostatic oil To top it off. Many people on here have said they use motor oil without any
issues at all.
I have researched many oils and the main differences are in the additives used. Motor oil and hydraulic oils use the same base oil. I would not use real cheap oils as pumps and motors are way more expensive to replace then using good oil.
If Bobcat has oil in stock at shop.bobcat.com, they ship to your door for free as long as you spend more then $99 and their oil really isn't any more expensive then other brands. You do however get a little piece of mind that the oil is high quality.
The chain case is just an oil bath so you can use just about any oil in it. I use the old oil from the hydraulics in the chain case since it has been filtered the whole time.
Here is a video that covers Bobcats new oils. Pay attention to what he says about hydrostatic systems. The last time I checked Bobcat still had the old wide temp range oil also: