There is a large nut on top of the screw that is probably stipped from running the screw down too far causing the flywheel to loosen up. The key and key way are most likely chewed up but nothing that can't be fixed. Get a picture of the top of the flywheel where the nut is perhaps you will see something. The threads can be restored on the screw and perhaps the nut can be salvaged as well.
The key way might need a little welding and some time with a die grinder but if the price is right it will pay to fix it. I purchased two fly presses from Grant and they both had problems but they are simple machines.