> When has any company been held liable for a customer modifying it.
All the time. Regardless, the liability is to their brand. If someone hears that a John Deere tractor blew up and set a field on fire, they avoid the brand. Even if it was caused by an improper repair.
> They already distribute parts to dealers around the world who service the tractors.
Just guessing here, but I imagine they do this in bulk to local service centers, via a regular distribution chain (on a semi-truck to many service centers) to manage cost. Distributing a part to an individual, or service centers they don't own, would require remodeling their distribution chain. My point is, it's doable, but not cheap, and customers will end up paying for this convenience in the price of the product.
> They already have repair documentation that they distribute to dealerships around the world.
That are used internally... Are your internal docs customer friendly enough to help them repair the most minute problem?
Like I said, I am for right-to-repair and I'd like to see manufacturers move towards these types of models, but it's typically basic market forces that cause manufacturers to act the way they do. Unless I see evidence that someone consciously chose the "No, lets screw over our customers for more money" option, I'm not going to assume mal-intent and start screaming "they're holding customers ransom!" from the hilltops.