Stripped my motor at the weekend, It was sticking every now and then and needed a tap with a hammer to free it. Took about 40 mins.
Undo nut on spindle holding rotating arm, and pull off rotating arm.
Disconect electrical plug going into motor.
Undo three nuts holding motor to mounting bracket and remove motor.
Remove 5 self tapping screws holding base plate and remove base plate.
You will see a metal drive wheel sitting on a white cog wheel, mark a line on both and the case, remove both.
On the side there is the drive shaft from the motor. Lift off black socket on top bearing. Undo 2 self tappers holding motor to gear housing. Remove motor and drive spindle.
Spray silcone / lithium grease inside gear housing.
Rotate drive shaft 180 degrees, grease and replace motor and 2 screws.
Rotate cog wheel 180 degrees, replace cog wheel and drive plate, grease.
Put back on gasket and cover plate and reverse removal procedure.
Hopefully the combination of teeth meshing in a new unworn part of cog wheel and re-greasing will give it a new lease of life.
I still carry a hammer , just in case!