I haven't tried it but kerosene is also recommended for cleaning out gummed up oil and it won't harm the finish either. I don't think I've welcomed you yet. Welcome to the forum.
Inspect your bobbin winder closely, I don't remember which machine it was but I had one with some old thread jamming up the bobbin winder too.
Sew Classic sell new bobbin winder tires and they're cheap. Probably under $1.00 to replace it if you think it's bad. Have you sewn with your 66 yet? I have a 66-16 and it's my favorite machine.
I've read here that you should buy your bobbins at Sew Classic too. I haven't yet but I can say the metal Singer branded ones I bought at Walmart have serious quality control issues. The plastic Singer ones seem to work better but I was at my LQS the other day and their metal bobbins looked better that either of the Singer branded bobbins I've tried. I'll buy theirs or Sew Classic's next time I buy any.
That is one pretty machine. Some of the best looking decals I've seen yet.
Rodney