For vintage machine parts I always use Sew Classic.com I replace the foot pedals with solid state ones but keep the original for re-sale. I give them a good clean up, there is a site on here or on youtube. I have never had a problem with the internal wiring but looked them over well before buying. Flawed wiring is a big no no for me. Greasy gunk, old threads, jammed parts, stinky smell can all be taken care of safely.
