Jeff
This is a common problem with cast parts. Most all the manufacturers had zinc pest issues, although it has become a lot less common in the modern era, but it does still occur. The manufacturers let impurities get in the molten metal.
Southwest
The wheel I used was a Bowser wheel I removed from a McCoy Little Chief. Someone had done a poor job of installing them so I got some McCoy drivers and put the Bowser ones in the parts box. The only issue is you would need to tap a larger thread to hold the CMC drive rod screw. Also on CMC, you need 4 ungeared drivers, not two geared and 2 ungeared.
Steve