I had a 401 I wrestled with for a long time. Since I was able to change the motor out, I knew it was not the motor. Scary? Well, I oiled and oiled and oiled. Oil was dripping from that machine. It still ran slow after a bit. Finally, I turned the machine on its side and ran it, I flipped it on another side and ran it and so on. I am thinking it may have been starved for oil in the bobbin area - at least that was the last place I oiled before it took off running. The bobbin area on that machine also has a lot of hidden frictions points. All I can say is keep oiling friction areas and turning the machine from one side to another and end to end - careful with external moving parts. Once you get it moving you will have to clean off all the oil and lightly oil where needed. It could be you need a motor.