I am no expert, but it seem the first step is to get the frozen one cleaned up and running. Follow Billy's tutorials to do this. Then do some side by side comparison stitching while they are both electric to see how they sew. I seriously doubt that there will be any need to replace parts on either of them since you said the shuttles and bobbins are still there. Those and the slide plate are often the first to go missing. The internal workings are so well made that unless someone tinkered with it or "adjusted" them in ignorance, they should be in good condition.