My 02.
Tap the motor - cost nothing and might help.
Disconnect the swing arm from the motor to the step (remove cotter pin and punch out the bar holding the two together). Once you disconnect that swing arm you can determine three things 1) whether there is binding issue (steps should move freely by hand) 2) motor is working (it makes noise) and 3) swing arm and related gears are working (swing arm moves when motor is humming).
If the steps are binding - lube/align or whatever you need to do to fix that. If the motor makes noise but the swing arm moves you can either replace the motor or take it apart and replace the gears .... s/b plenty of post on both if you use the forum search feature.