I was always curious about this practice since over the years in general, they've consistently bent over backwards to help, sending replacement stuff time and time again, never asking when or where it was purchased. But whenever this came up it was always nope, only it they did it on 6i and above.

I ended up just using the opposite side's arm as a template on aluminum stock and making my own. I guess Dan has more patience than me by casting it.

It's a pretty straight forward mod, it's just a spring loaded arm that pulls the gimbal down to center. All the mounting pins, etc are there, you just need the arm and spring. That's what makes Horizon's reticence more annoying, just throw the part in a bag with the spring and they would probably sell tons of them. The only thing that comes to mind is since they have such a liberal warranty policy, they probably don't want to encourage cracking open Tx cases.