Retrofiting an old big milling machine

I have contacted diamand polymer and there is a communication problem.
I asked them about their products they answered me after 2 weeks with a generic mail
and after that i asked them many times for EU moglice supplier without any response.
Seems more easy to buy moglice in US than EU.

Ballscrews for X/Y 32 or 25mm are cheap but 65mm for Z is expensive.
The brushed DC motor that have now is 100V 26A 1000rpm moves up/down Z axis
without problem but i have big servomotors > 3kw so motor is not problem for Z.
The question for Z axis is the backlash if keep existing leadscrew the weight
of table theoretically eliminate backlash automatically..
Exists any use case that backlash can appear on Z axis with leadscrew ?
If i can hold Z axis leadscrew then X/Y is ok to replace leadscrews with ballscrews.