Jubilee 3 point hitch won't lower

Can you move the lift arms at all? You should be able to move the lift arms up a little more even though it is in the up position. If you can't move the rock shaft at all by lift up on the lift arms with nothing on them it is possible that the rocker is broken internally where the ram rod goes to lift it. I guess it is possible that the control valve could be stuck but that is unsuall too.

Yes you can see if the control valve is stuck by going into the right hand inspection plate. And you might even be able to look at the lift rocker socket with a flash light and a small inspection mirror to look up with.

If the control valve is going in and out and there doesn't appear to be anything broken then the only other thing I can think of would be the unloading valve stuck in the up position but like I said it would be very unusual. I have never seen one stuck in the up position and I have seen plenty in the past 40 years.