history and good old gut feeling. Condition and loads of history with money no object kind of ownership.
What i do with cars with expensive parts is i build up a car slush fund, over time you can dip in to the slush fund to maintain it. Build up the car slush fund to a level that if anything bad happens u can cover a big chunk of it. Like a personal warranty where the money is in your bank and not a warranty / dealers bank account.