opalstar, the large spring that you can see in the fourth pic of post #30 is the one you have to worry about, I think the smaller springs you're talking about are the motor brushes, which you don't have to mess with if the motor works OK. I have the feeling the spring is slipping off the little nub on the motor it seats on as you put the motor back on, it takes a little finesse to get it right.

The old straight stitchers usually manage soft leather with out any signs of working too hard, most capable machines will. I don't think I would aim for anything thicker than hand bag weight leather. You easily know when the machine is working too hard.

Does anyone know if this is the right replacement pulley for this model?

Yes, after testing it a little bit I agree. Thank You