I replaced the heater core in an old Cadillac once, and had about half a coffee can filled with leftover screws. I had to remove most of the dash to get to the connections, and it was impossible to line up many of the screw holes that went through 2 or 3 piece of plastic to reassemble. It worked, and didn’t leak, so I was happy, but I will stay away from watches. Putting in a new battery and setting the time and date taxes my watch repair skills to the limit.
When I was a kid my Stevens 22 semiautomatic quit extracting. My dad and I took it apart and found the broken extractor. Didn’t have a source for a new one so we cleaned everything and reassembled it and kept the broken part for later. Turns out, it worked great without it so we forgot about the part.