Broken Hydro release knob


Hi all,
I had to pull the rear end off my '68 Ford 120 last winter to repair a leak in the hydrostat, and broke the knob for the hydrostat release when I tried to remove it.
The knurled brass insert is still on the shaft, I assume it is threaded on??? It won't come off, even with heat. Can anyone confirm for me if the shaft the knob attaches to is threaded?
I haven't been too aggressive with it yet because I don't want to ruin it if I have to try to reuse it in some way!
It'd be great to be able to release the hydro easily again... I saw a knob on a JD parts site that looked identical.