What does the Tri-flow do to the hardened film that machine oil can't? I'm not familiar with Tri-flow.
My 201 sews a little stiffer than my 15-91. The difference is slight, but since I know what a Singer machine is supposed to feel like, it bothers me to have the machine drag, even though it is only slight. I keep wanting to push the knee lever harder but it already has the pedal to the metal. If I didn't have my other Singers I wouldn't know the difference.