Hi..... if you manage to take the nut off the screw without the balls dropping out.......you'll need a dummy plastic tubular insert to follow the screw in as you wind it out .......this will keep the balls in the nut, but you won't be able to see if the balls are in bad shape.
I would say that it appears that you have swarf or chipping in the nut and need to run some Kero through it while it's off the screw.
At the same time examine the screw closely with a strong magnifier for ball denting or rough spots.
if you do get the balls out and do an examination, measure them and note if they are all the same size.....some....about half...... will be smaller by a couple of hundredths of a mm as they act as spacers alternately to enable free running of the nut.....I could be wrong on that score but I think this is how it works............balls crowding against each other if all the same diam will only jam up due to friction.
Then you will also need to reassemble balls in the nut.......best of British.
If you had some serious crashes you may have ball denting in the nut or balls that are rough......replacement nuts are quite cheap if the screw is undamaged.
A lot also depends on the precision that the nut may have and the preload value too.
I have a thought that if the screw was in good nick, then getting two new ball nuts and fitting them to the screw would not matter if they were slack as the two nuts can be made to have as much preload as you need by backing them against each other and securing them, whereby you'll have adjustable anti backlash properties simply and cheaply.
Ian.