I just saw a fragment of BTTF where marty keeps hitting hit head to the door because of a bad gas spring, something hit me:
http://www.imdb.com/title/tt0088763/trivia?tr0798779
"The script never called for Marty to repeatedly bang his head on the gull-wing door of the DeLorean; this was improvised during filming as the door mechanism became faulty."
"The gas-powered struts that hold the De Lorean's gullwing doors open would fail during the course of filming a take, so crew members had to be on stand-by with hairdryers to warm them up to stop the doors from drooping. "
Why? The car was 2 (TWO!) years old at the time of shooting the BTTF movie. I've had my struts for over 10 years and they're still tight as a [beep]. Were the original struts THAT bad?