Not to worry, Percy. The window lift gearbox comes out of the doors quite easily so you can mess with it on a bench. You actually have 3 of them: the headlight erection mechanism is identical to the window lifts. What happens is either the plastic gear shrinks with age, causing extreme stress on the gear's metallic hub which cracks the plastic. Or the factory grease inside the gearbox turns to a brick. Taking the cover off reveals which. There are bronze replacement gears available- I suggest replacing all three.
The DC motors have brushes that can be changed and loosening the window guide bolts allows the windows to be realigned so it doesn't take so much power to lift the glass. If you're going to keep the car forever, Ted MItchell's Vader Window LIfts are an excellent investment that solves ALL the problems. They lighten the doors by 6 lbs/side too.