There doesn't seem to be much aftermarket parts available for the ZF transaxle, whether fitted in a red,blue ,green or orange tractor!
It would be interseting if the price of parts for lets say a pto clutch pack, and the complete brake kit ,including the pistons or pressure plates that can get scored , could be compared for a 150 ish hp Kubota, and the other common tractors.
The ZF transaxle is well engineered and generally will run to very high hours without needing parts. And you obviously don’t know the right aftermarket suppliers!