A house built in 1968 has had an opener swapped out once, maybe twice already, and each swap left wiring, brackets, or a door-mounted bracket plate from whatever installer worked that job. The most common issue we see on this kind of stock is a mismatch between an old steel door - heavier, thicker gauge, no insulation - and a newer lightweight opener that wasn't sized for it. The opener strains, the gears wear fast, and within a year or two it's slipping or stripping.
Cold is the other factor. This part of Minnesota sits in a severe cold climate band, and old grease in an opener's gear housing thickens hard in deep cold, which is part of why older units struggle to lift on the first cold mornings of the season. Combine that with a 1968-era door that's heavier than anything made now, and the opener is working against two problems at once, not one.