While I bow to your experience Jazz, and I do know that my knowledge of this machine is limited to what I see on those pics . Never seen one in the flesh, Never used one.
But having replaced leadscrews with ballscrews in a different application, I found it no big deal , and it looks to me as if a BF on the outer end of the leadscrew/ballscrew would at least eliminate any end float in that screw without being a challenge to mount.
I dont see enough detail in the crosshead pics to know what is in there but it is hard to believe that an adaptor for a ballnut could not be accommodated. and £ 30 or so is not a massive outlay to keep the machine running reasonably while Petesos (like me ) continues his learning process.
Lets face it , once he replaces this machine it is consigned to the scrap heap.
I am only offering an economic solution to his immediate problem.
If he has the funds to splash out on a superior machine then all well and good ,
I was only suggesting this as an interim solution , which reading between the lines Petesos may be seeking