I tried to page through the thread to see the full manual for a 5513, but didn't see anything except some specific links to parts and some references to a person named Ruby. I also saw the link to what different factories best produce what. That said, are there also "factories" and reps for the parts? So for my example of a Uboat is there someone who reps the cases or someone who reps the movements etc?
In your case. Your best bet is buying a complete watch from a trusted dealer e.g. PureTime. Here’s a link to the Uboats they have available:
https://puretime.io/watch-brands/u-boat.html?limit=all