Clearly a product you have has deteriorate. Kind a like your 1990 car. They did not paint it with rust on it, but it did rust later.
That is not an apt analogy. The zinc rot/pest is due to impurities in the casting, resulting from poor quality control. The product will degrade regardless of how well you take care of it. On the other hand, in the right environment, and with proper care, a car will not rust. If it does rust, you can sandblast and repaint—if you catch it early enough—or excise the offending material. Not so with zinc rot.