Hi again Linda :- )
I see you haven't had a chance to reply yet. The advice might feel a bit radom, particularly if you can't figure out what's wrong, but it's all spot on for trouble shooting the issue and I'm sure you will have it sorted out before to loong.
I have a friend who insist the small 28 is her best stitcher and it does run very smoothly. At times it set up as a dedicated buttonholer and since it's a hand crank its' also a favorite when precision stitching is called for. She also has a 201 for comparison, which is my favorite model. I have never had a smoother running machine or easier machine to work on than my 201. Some of these old machine are a joy to work on (I promise!) I hope your 128 will be the same for you. Let us know how you are doing.