I love the car analogy - have made it a few times myself. It gets better - suppose you find the cause of the problem, but by the time you do it's knocked 3 other things loose, or fixing this thing just revealed the other 5 things wrong...

The living will sounds so simple, and he has one, but then the question is "What is this, what does it mean, what are the odds of x, y, or z, and what would he want - we never talked about THIS situation..."