Stewart Alco 630 Drive shaft problems

The ends have broken off the drive shafts of my Stewart Models C630's. Is this a design defect? The little plastic ball at the end of the shafts has
split and now the locos don't work. Is this a known issue?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.