Garage door needs a push or pull to start opening/closing
Though they're 20+ years old, they didn't miss the plastic bug. It's likely that your drive sprocket on the one is worn down &amp; begin to miss. However, a little more specific &amp; much less involved to remedy to your symptoms would be to play with the up-force &amp; down-force adjustments.

Usually, clockwise is to ramp up &amp; counterclockwise is to ramp down. The openers develop flat spots on the clutch &amp; screwing-in or clockwise reseats the contact points. If it works it'll work for years, I'm going on 5-years now with my current one &amp; two others I had before got 8 &amp; 10 more years before adjustments didn't work anymore.