If your door is groaning, sagging on one side, or won't lift past a foot before stalling, you're likely looking at a spring that's lost tension or snapped outright - common on houses from this build era where the original spring was never replaced. A door that reverses right after the floor instead of closing fully often points to worn rollers dragging in a track that's seen 30-plus years of use.
If the opener runs but the door doesn't move, check the drive gear and the chain or belt connection before assuming the motor's dead; on original 1980s-era openers, the gear is usually the first thing to strip. A door that's suddenly heavy to lift by hand, even with the opener disconnected, almost always means a broken or badly weakened spring, and that's not a DIY fix - the spring is under enough tension to cause real injury.