> Those bits should be easy, unless the OEM was tragically stupid.

Well... just look at Tesla. A lot of their parts don't come from the classic supplier-OEM delivery chain model, but Tesla makes as much as they can on their own. It saves them a bunch of money, both when it comes to the profit margin of the supplier, and being at the whims of their supplier, but it is nasty for the customers when there simply is no parts OEM that one could go to when the vehicle manufacturer goes out of business or refuses to support the car any further.

> Where you'll get into trouble is when you need replacement computer bits

Oh hell yes. New EU law is particularly to blame here. OBD diagnosis always was nasty enough, you virtually always need to buy expensive diagnosis software and hardware (e.g. Mercedes XENTRY, VW ODIS, BMW ICOM)... but the newest requirements enforce live digital signatures and anti-tamper checks. Nasty as hell. And the buses itself... it's no longer just one CAN bus doing everything, not since the Kia Boys, it's multiple buses of different speeds, some using encryption on the wire, all making diagnosis, troubleshoots and repairs much more difficult than it used to be.

And that is before getting into the replacement parts issue itself that you wrote up.