Mid-70s hardware replacement history
That gap matters because a door built in the mid-70s is more likely to run on hardware that's been replaced once already, or never replaced at all. Before you call anyone, you can do a few things safely: pull the release handle and see if the door moves smoothly by hand (it should, with even resistance, not a jerk), check that the tracks aren't visibly bent, and look at the springs from a distance without touching them.
