I have a very old Donkee ball spinner. The threaded rod that feeds from the under side of the ball cup to the bottom of the spinner where the large belt pulley attaches has gotten pretty worn from over time. The "flat spot" where the set screw clamps down is worn enough that I constantly have to flip it over and try to tighten the heck out of it in an attempt to keep it from slipping. Any idea on where to find a replacement or any kind of fix to attempt?