Your finish isn't 'japanned'. It's baked on enamel and very tough. I scrubbed one with a toothbrush and Dawn dishwashing detergent, making sure none went into the machine and rinsing and drying well very quickly. If it's been around a smoker, it takes some cleaning. I don't know about the rust - I've never had any except on one bobbin and I'm going to throw that away.
Caroline and Joe, my Admiral machine that looks enough like my Necchi to be its brother was made by Brother in Japan. Just to confuse things even further on these Japanese made machines.