Builder-grade openers from the late 1970s and early 1980s were built to a price point, not a lifespan. The gear-and-sprocket assemblies inside those chain-drive units use a nylon gear that's meant to wear down before the metal motor shaft does - it's a sacrificial part by design. Forty-plus years in, that gear is usually gone, and on a lot of these units the capacitor that gives the motor its starting torque has dried out right alongside it.
The mild temperate climate across this part of the service area doesn't accelerate things the way extreme heat or humidity would. There's no monsoon season or deep freeze cycling the plastic and metal apart. What you get instead is straightforward age: components reaching the end of a normal service life on roughly the same calendar, because the houses around them were mostly built in the same few years.
Household income here runs lower than the broader service area - about $96,190 versus $104,565 - which is worth mentioning because it shapes a real decision: on a unit this old, a straight repair of the gear and capacitor is usually the better call than a full opener swap, as long as the motor itself still tests sound.