Hello mike48130,
If the hydraulic motors and gear pump are cracked and leaking oil they are worthless. The oil cooler and fan motor assembly if cracked as well will be of no value to you.
The problem is simply one of economics only because your time is worth something and your investment will be labor and NEW parts
Flushing the oil cooling radiator and installing new hoses as the old ones are no longer viable due to the aging of the hose rubber on both the exterior(cracked( and interior(dissolved/cracked). The replacement hydraulic motors and pump are not worth rebuilding as they will have to be completely rebuilt from replacing the hydraulic pump/hydraulic motor shaft to the end bearings and seal sets as well as the BSP o-rings on the hydraulic fittings if used on this model.
The hydraulic fittings may also be cracked as well from the ingress of water into the system.
Getting involved with out of state hydraulic parts suppliers will be be more of a headache than its worth only because of the distance.
If you want a "new to you flail mower" checking tractor house for a used one for your mule is a better more economical option simply because it it a rear PTO powered unit.
Another option would be to invest in a new 48 inch Vrsimo flail mower as they are $3,800.00 plus a set freight cost(complete-minus PTO shaft) from the builder in California and parts are available and less expensive.
These 48 inch units can be front and or rear mounted so that is also a plus if you have a small mule like a 4 wheel drive ferrari tractor or an Antonio Carrero mule with a front three point hitch.
If anything just save the knives and invest in a flail mower with the same size and type of side slicer mower knives that has the same type of flail mower rotor and knife mounting station type..