is it hard to turn the key in with the key in the door lock cylinder? I would take the door panel off and try unhooking the rod from the door lock cylinder and if its easy to manual unlock and lock then replace the lock cylinder, just rebuild it with new tumbers of the same numbers. I can help you with that on the side.

If its still hard to manually unlock and lock with the rod disconnected from the door lock cylinder then reconnect it to the door lock cylinder and disconnect it from the door handle and try it. You only have a few options here on manual door locks. On power door locks its either a door lock acuator or cylinder binding.