It's debatable what part of any manufacturer is 'original' nowadays! The car is made by a 1,000 or more specialist companies. Take an engine. The electronic management control is Bosch. The valves, gaskets, piston heads, cranks etc are all specialist supplied components.
TVR got into the realm of 'trying to reinvent the wheel' a bit too often. Their engines were fantastic for the budget but a tad unreliable. Using component suppliers gives you the opportunity to draw on a vast research and skills base no single manufacturer could ever attempt to replicate. The job would be too vast an undertaking and too expensive.
Are manufacturers just 'assemblers' and organisers of the final product. Are they just the engine? Seems to me manufacturers are more 'designers' than benders of metal nowadays. Nothing against that so long as Chris Bangle isn't doing the shaping!