The majority of things in patents could not be kept secret. What we end up with is disposable products because every part is patented so you can't make replacements or other devices that are compatible.

For most things, feel free to reproduce patented parts for your own consumption, just don't give them away or try to sell them.

Thats a non answer. I don't have metal working tools sitting around in my shed that would let me whip up a replacement part for things. As a society we throw away so many things because they contain patented parts and the original company wont sell replacements or they sell them at enormous prices.

Hopefully in the future metal 3D printing becomes common and cheap so we will be able to source replacement parts from torrent websites.