when a stepper unit won't step easily with your finger, it's time to take it apart and clean all the old dried grease off the moving parts. The coil just pulls the arm/pawl back to grab the next ratchet tooth ... the spring turns the ratchet when the coil unpowers and the problem is almost never the spring assuming it's the right one.

if you are lucking, just cleaning the contact plate rivets will make it work smoothly, but most likely you'll be pulling it apart to clean the ratchet shaft, hole it goes thru and the pivot points on the step-up arm/pawl.

where the washer is hanging in the shaft slot is supposed to be a hairpin ... or maybe the spring end goes there not on the end of the shaft ... I forget.
The spring should be perpendicular to the shafts. Someone will let ya know.