This is my favorite side project that I've ever heard of. It's so cool how you stumbled into it and there's a lot of scope for other products too!
He was originally in the business of repairing these machines and then discovered he could no longer buy these parts from the OEMs so he learned CAD and CNC and injection molding and started making them a few years ago. He has a 3D printer for prototyping, but he needs to injection mold part of the final product because there is no filament in the particular material that he needs. His business has transitioned from repair to manufacturing and now he mostly sells replacement parts to other repair shops.
I don't want to disturb his business by talking about it in detail, but the point is that I think there are and will be many opportunities around repair parts that manufacturers are unwilling to provide because they'd rather be selling new machines. Aside from the environmental impact, that's fine since there are many people who won't go the repair route, and then there's a secondary market for those who will make parts and repair the machines.
There is a solution to so many problems here (creating usually unavailable parts for machines/devices/products) but the problem is knowing which parts are in demand and currently have no supplier.
A maker would need to have an interest or hobby in such a device & discover a need for the item for it to come into fruition. But just think of how many general 3D printed parts could be printed as solutions for so many products out there that are going unmade.
I was not commenting on the quality of the work. BTE, saying the Chinese quality must be automatically shite is a ridiculous idea.