On machines that sit for a while the lubricant becomes sticky.
Check the reel disc slots for excessive greasy build up.
If these slots are sticky, the kickers and slot arms will be effected.
Check to see in the reel shaft is installed properly into the chassis. If its miss aligned this would be a problem.
With the reel mechanism on the bench and reels out, push the wiper arms back, they should spring back.
If they move slowly, clean the wiper boards, they also can build up with grim and slow things down.
(TEST NOTE) The arms will most likely exceed the guide slot and not return without manually realigning them.
Last week I had to clean a reel mechanism 3 times before it would kick and stop the reels properly.