5. There Were Two Cars In 1885
When the Doc gets stranded in 1885 he leaves a letter giving instructions to Marty where to find the Delorean and what needs to be done to repair it. Sure enough Marty, along with 1955 Doc find where the car was abandoned and fix it readying Marty to return to 1985. Before this can happen they discover that the Doc trapped in the past will be killed days after writing the letter so off Marty sets to the old west to rescue Doc Brown from an untimely death. A run in with a group of native Americans leave Marty with a punctured gas tank and no fuel to get the car up to the needed 88 mph, and sets up the whole films plot of finding a way of pushing the Delorean with a train. None of this was necessary! When Marty received this puncture he and Doc could have just made a short trip to where the version of the Delorean that Doc arrived in 1885 was and siphoned off the petrol! There's no reason to believe that the Doc had run out of petrol upon arriving in 1885, or any good reason why he would have emptied the tank before hiding it in the cave where he instructed Marty to find it. Between the two cars that existed in 1885 Doc and Marty could have easily had a working vehicle. All of these car repairs weren't actually needed either which bring us to the next point...