I'm not 100% sure, but I think that freewheel has plastic seals over the inside and outside bearings. If they're still flexible, you can pry them off with a small screwdriver. (If they start to tear, stop- there's no way you'll find replacements.) With them off, soak the whole shebang in kerosene, then dry it off, then run plain 10-weight oil into the bearings. Pop the seals back on and it'll be good for another 50 years.