"Quiltingweb, I know you have gotten several answers to this, the tri-flow, heat, all the oiling, but have you really taken the time with a flashlight turning the machine every which way with the slide plate and needle plate removed to make sure there is no thread, hair, lint caught in the hook/race/bobbin area? Also, oil the needle bar really well and keep trying to wiggle it - after you are positive there is nothing caught in the bobbin race area! Cathy on here told me that the machine sticking at times usually meanes the needle bar has lint around it or needs oiling.
Nancy"
Yes. I was able to move the needle bar by undoing a screw. It was a bit gummy at first, but I was able to get the needle out of the way so I could then take apart the bobbin area to make sure there was nothing stuck there. I tiny bit of fluffy lint, but nothing that would jam up the area. The culprit seems to be on long rod that runs the length of the machine, underneath, from the gear on the left to the bobbin spinner on the right. Everything else jiggles slightly except for that one rod and its gear.