Retrofitting a 1986 Maho MH400E

There is a ball supplier on Amazon.

www.amazon.com/Ballscrew-Screw-Balls-0-1...3-1699/dp/B0070I68GU

Thank you for that, the size is 3,5 mm. like those
www.amazon.com/Diameter-Chrome-Steel-Bea...mm+Bearing+Balls+G10

For a ballscrew you want to be more accurate than just "3.5"

The vendor in the link I sent does them in .001" increments, but only around a 1/8" nominal size.
www.amazon.com/s/ref=nb_sb_noss?url=sear...+Screw+Balls+100+pcs

More than that I think its suggested that the balls be in alternate sizes (spacer balls and load bearing balls)

I think that alternating might be done also when fitting oversize balls in order to keep the train length the same.

The micrometer reeds 3,499. The only solution is to send samples to the supplier and he will responsible to proper measure the balls with the his advanced measurement tools, and then send me the proper sized replacements. Or even better solution is to find some company on Europe to send the whole ballscrew, to replace all the balls and seals. The only one that I have found has never answer back.
John