That's good advice from Dan about safety but maybe not so easy to apply in your case. Those axles, like mine, are the earlier version which are different from most of the ones on ebay for later W111s, W108s, etc. They might be interchangeable but certainly have a different mounting for the brake caliper. and dust shields.
Maybe you can tell us any theory from yourself, or the workshop, as to what happened. I have just rebuilt my stub axles and Colin has just rebuilt his and we are both amateurs who may have missed soemthing. The innner bearing looks absolutely fine which suggests there was grease. I assume excessive preload would affect the outer bearing only as that is where the adjustment is made?