Two items here:
First of all, in something like a front axle which does not involve pumping the fluid through small orifices, lots of pressure, etc. I think the main concern is just keeping the parts covered with lube. The heavy gear oil will work just fine, IMHO. I wouldn't put it in the hydraulic system, but in an axle, all it has to do is cling and flow. Any heavy gear oil will work.
Secondly, my CC dealer has a rather low opinion of the Cadets that they currently carry in the CUT size. The like the mowers just fine, but not the tractors. They also have a less than stellar of the past several years of CUT Cadets. What model/year of the Cadet CCs were basically Mitsu's and how different were they from the Mahindra 15 series we see now. Are they pretty good tractors or should I not even look?
I'm asking because CC went to bat for me with Kohler a while back over an engine issue and got me a new engine when the dealer couldn't and Kohler wouldn't. This was in an old Cadet 109 lawn/garden tractor.