Recommended Lubricant:
Elbow grease!
My PN-4, bought with my 1974 Model L, was in worse shape than that. Careful disassembly, cleaning, buffing (by hand - whew!) and reassembly with a new brushroll made it very nice indeed.
Even though the result of reconditioning that one might not put it into the same pristine condition as the vac, you'd have a usable PN that would do until you find a better one.
P.S.: The buffing was done with Brillo first, to remove the rough oxidation and start polishing. Then came Nevr-Dull, to begin bringing up a luster. Last was Brasso, for a good shine. Not the same as machine buffing, but it made a helluva difference on a very distressed PN housing.