Yeah, good idea.
Under WTO rules, car parts would incur a 10% tariff every time they cross an EU-UK border. So, in the case of the BMW Minis, the crankshaft crosses the channel 3 times so thats over 30% added to the cost.
Or the Bentley bumper which is made in Eastern Europe, sent to Crewe for further work then back to Germany for finishing and then back to the UK for fitting. Then there's the fact that these factories carry no stock. They operate on a "just in time" basis so cannot afford any delays at border crossings.
Those are just 2 examples. Other car parts cross the channel many more times.