Getting just a little scattered, but yes I found your other thread and that certainly looks like a 201.
I think jmiller (joe) posted some Idea's in that thread. Certainly the cheapest and most likely "out of spec" part would be the bobbin.
Class 66 bobbins should be cheap and plentiful. I would follow other recommendations and try some quality bobbins, and of cour make sure your machine is clean.