The manual section has the owners manual for the 1862 (similar animal...). According to the manual the only fluid you can use is "Cub Cadet Hydraulic Transmission Fluid" - if you try to use anything else, the wheels will fall off and the whole thing will catch fire
I'm sure someone more knowledgeable about cubs will give you a more helpful answer. The manual says to use fluids that comply with IH
B-6 specs. You might be able to research and find other fluids that qualify...
Seriously though, I generally use Deere Hi-trans in most of my stuff - I buy it in-bulk for my big tractor... OR I've heard you can use ATF as well. Biggest problem is mixing what you put in with what's already in there. Some combinations may not play well together. IF your not really sure what's in there, maybe flush, put on a new filter and refill with new fluid of your choice.
You could also have some play in the mechanical linkages between the lever/pedal and the transaxle. Not sure about cubs, but on some of the deere's, you would get creep or speed fluctuations if some of the pivot points in the control lever had too much wear in them.