I have purchased one of these older machines and it’s not in too bad nick. The main problems are one sticking button and rusty needles. I’ve just removed the needles and some are quite badly rusted. After a wipe with alcohol to remove oily residue they have been put into a jar of 10% citric acid to see if I can shift the rust. I plan to leave them there for about an hour and take a look.
I have a fond memories of these machines; Jones KH588 machines were the first ones I used at college when I started my degree.
I’ve just made up a new sponge bar using a kit from Xena Knits. https://www.xenaknits.com/product-category/sponge-bar-kits/
These not only save money, but it’s environmentally preferable to reuse the old bar.