I am using Amsoil synthetic ATF in my BWVelvet Drive. The heat reduction has been quite significant. With hydraulic boxes, heat is a killer to them. The cooler you can keep the oil
, the more miles the thing will run for.
Is the Nanni under any Warranty? If it is, make sure you use the oil the manufacturer specifies. If it is out of warranty, then a good quality Deisel oil. Depending on your climate, a normal 24W40 would be fine. But if you experiance extreme cold, then a 10W30 or 40 will be a good choice. Once again, I use Amsoil 20W40 in my Perkins
6.354. It has made the engien much quiter. Shell Rimula and Castrol Magnetec are also good oils. Valvoline made a high performance Deisel oil as well. There are heaps on the market, just make sure you get a real good rating and don't penny pinch. Good oils tend to be the more expensive ones.