The binding feeling in a 500 or 400 series can be old grease gummed up on the big nylon gear on the balance wheel - pull that balance wheel off and re-grease it.
Might be thread or lint or (like my 404) old rusted and stuck lint in the bobbin case area or under the feed dogs.
The metal gears I usually found to be bone dry, not gummed up.
Cam stacks gum up and get stuck.
After you've oiled / cleaned / lubed all else, only then mess with the motor (you don't need to remove it):
Another cause might be the motor itself. It will be the top bearing in the motor. Place one scanty drop of sew mach oil on the shaft and let it run down in to the motor, then run the motor gently until it frees up. Just a little oil. You don't want to damage the motor by thinning out its grease too much. Just a drop to de-solidify the old grease.