I do not like to take the main moving parts off of sewing machines. However, sometimes you have to. My rusted up 99K was one such machine. In order to get it de-rusted and functional I had to disassemble the bottom end and pull one of the connecting rods out of the pillar. It just had to be done.
If I had your machine I'd just take it apart. You can't hurt it much more by doing so and you have a good chance of getting it fixed.