I am he as you are he as you are me and we are all together.

OR

We'll be fighting in the street

With our children at our feet

And the morals that they worshipped will be gone.

Michael,

Doc still had the gasoline in his DeLorean that they could have siphoned out and used. They didn't need all of it, just enough for one run. If it was used for that, no blown manifold at all, Marty goes home, end of story. The oinlyproblem then would be the fuel line with an arrow init, which I'm sure Doc could fix.

Alternately, saying that the manifold had been blown, Marty could've gone back to 1985 with the good DeLorean, bought a manifold, and brought it back to Doc in 1855. Problem solved.

Only one. It's in BTTF 3 and actually kills the movie. It occurs when they're trying to get the DeLorean going and blow out the manifold. They have a spare. It's in the DeLorean that Doc buried. There are two DeLoreans at that time: the one Doc arrived in and the one Marty arrived in. They could have used those parts and drove home. No train, no love story, basically no movie.