For my 2010 model year Cub Z-Force ZTR with 20hp Kohler Courage V-twin, Cub Cadet recommended Rimula 15w40 for the Hydrogear ZT2800 drives AND the engine.
Obviously Kohler sticks with the generic 10w30 recommendation like they have for decades.
I used Rotella 15w40 because it's an easy to source, relatively inexpensive oil that's proven to work well for so many applications.