> Just grab one before it goes to assembly line, ship it with the actual completed machines to a distribution center

So customers can only order replacement parts while assembly lines are currently doing production runs?

This is sort of liking saying “how hard could it really be to do a special software build for one customer?”

I guess it depends on how you CI and build process is setup. Caddy does an excellent job of doing per-customer custom builds.

If you just "grab one before it goes to assembly line" this will likely have a huge impact on the assembly line. Factories put a lot of effort into managing inventory of material. Lead times on parts can often be in the months if not years. If there are unexpected shortages of parts and subassemblies, the hourly or daily costs of a line down can be enormous. Shipping one of something to an end consumer is usually a completely different supply chain than shipping containers full of finished goods to distribution centers which then go to retail. Taxes, tariffs, shipping methods, etc are all completely different. You can't just commingle things like this easily.

We once had to drive special parts for one car by taxi cab to the factory, in single figure quantities, to not let the line stop and pay the fine... "just in time" production can be hell...

What if it's no longer being manufactured or on assembly line? HOw do you grab it before assembly line?

And comingling parts with completed machines? Heh. You have no idea of the distribution chain of b2b retail goods vs b2c service repair and such.

6-8 weeks repair time is still common, especially nowadays.