I've had my x320 now for one month and I've put on 22.5 hours already. I've also thought about putting synthetic in the trans as well as the motor. Perhaps in the future I will. I've been reading quite a bit on synthetic and see no drawbacks to it at all, but only positives. But, I have to believe that if John Deere wants us to use regular oils - then there must be little if any bad effect to the trans or motor by using it. They must have mechanical engineers who study things like this........ right?
But then........
The troubling thing is, if Tough Torque is recommending synthetic, why is JD using regular?
The other troubling item is that JD recommends changing the trans oil in the x360 at 50 hour break-in, and then every 200 hours. Granted, the x360 is a different trans, but how different is it really from the x320 trans where JD recommends never changing the fluid? Since the x320 trans is smaller, you'd expect it to be changed at the same schedule.
My old Wheelhorse that I bought new is ancient. She's a tired old rat-trap but still runs. I expect this x320 to last nearly as long with the same servicing, but by that time I'll be senile anyway....maybe.
I love the x320 - no complaints - it's a great piece of quality and I'm glad the money I spent on it is mostly going to American workers.
rich