If you are breaking the upper actuating arm there is a problem somewhere in the powder/shot metering system.
First, make sure everything is clean. Remove the top plate, the powder and shot gears and the shut-off plates. Clean or blow out all powder and shot debris.
If the rack does not move easily then loosen the two front thumbscrews to relieve the pressure on the powder seal. If the powder seal is causing too much drag you may wish to consider my Machined Aluminum EZ-FILL base. My powder seal is designed to seal properly with minimal drag.
.They must have change something since mine was built because my upper actuating arm is not pot metal.
Other things to check is if your powder and shot gears are properly aligned with the gear rack. (timing marks aligned with each other)
Top add to Surfers post, put a little graphite on the bottom of the gear rack ( after his recommendations) and make sure the nylon screws just barely keep the the gear rack from moving up and down. I even leave mine with just a little play.