Humans equal non perfection results when dealing with mass production.
Fact of life unfortunately.

Your Gene Simmonds head might be perfect Nino.

Stern and every company on earth has a warranty for a reason. Nothing is perfect.

Even your restoration business would offer warranty Nino.
Just incAse you or another human involved in your business makes a mistake or doesn't see something during the massive labour task you and Stern share. Is that a fair call about warranty and your warranty.
It exists cause people strive for perfection but sometimes don't hit the mark ?

I think the quality issue has existed since pinballs were invented and probably wil exist forever cause humans build these things. What can u do but try your best ?