I'm not an expert here but...
I thought ND was formed after ZF was sold. It is not the same Company or the same design. Am I wrong? I wouldn't think that ND could/would build the replacement part you needed for your ZF tower. I thought you were contacting ND for advice.
When I dealt with ND on my tower I will say that their customer service in the way of returning calls and emails could have been a lot better. And, the "lady" who answers the phone was not always the most helpful which is why I always dealt directly with Wayne Hartford, the owner.
So let me get this straight. You have a broken ZF tower with apparent inferior materials/workmanship, and you unload on ND (not your tower manufacturer)? If you were going to be mad at anyone, I would think it would be ZF and MC in that order.
I wouldn't have the old tower welded until the MC dealer or ZF has a chance to inspect it (if you hope to get any satisfaction.) I certainly hope it all works out in your favor Mitch.