And now, for something completely different....

What you have there is a rusty hunk of junk. The seat has the same "patina" because all that's left is the steel shell and it too is a rusty hunk of junk. There's no finish left to preserve or conserve.

If you are suitably motivated and funded, get it restored (de-rusted, repainted, new seat cover, wheels and tires,...). Parts can be replated if desired (ka-ching$), or just painted. Need I say, it needs a new chain.

I do agree to tread carefully on doing anything that cannot be reversed (basically, cutting metal).