>at the end of the British Leyland body assembly line men with large hammers would whack the doors from below to make them close properly.

Not that your point about inherent complexity doesn't stand but having to whack body panels to make them fit just means the dies are at the end of their lives. They certainly would have fit without mechanical persuasion when the dies were new. The hood of any late 90s International S-series is a good example of this.