Whoa..so all your chrome bits are now painted, also? That is certainly the problem. Paint glues stuff together pretty well. Ever try to open a window that has been painted shut? Rust should not be the result of a paint job either.
Much as I hate to say this....How much do you love your machine? If you find an old sewing machine guy to do this Big IF. it will cost a lot. Younger techs generally don't have much interest in our old beasties. 66s aren't so rare that you can't find a working one. And don't take it to the same "painter".
I was thinking "easy fix" till we got more details.