No Tri-Flow ...... ewwww! I don't use T-F for cleaning but it's all I use for oiling.
You shouldn't ever take the screw out of the bobbin latch lever. That part controls the gap between the bobbin case and latch. Hopefully you got it back in exactly where it was. There is a proper way to remove the latch.
Sand paper and oil .... oh my, that's worse than pumice laced cleaners.
Glad it worked out for you, but I think you should re-think some of your techniques.
JMHO
Joe