If you wind up with an extra seat let me know, I just picked up a Golden Flyer and its missing the correct seat. And in the past some bonehead cut off the back half of my rack, so I'm looking for one too!
All you ever wanted to know about oxalic acid...well almost.
I've used oxalic acid (crystals) for quite a while and have had impressive results, especially on chrome. It works pretty quickly too, although I tend to let parts soak overnight.
It does leave a yellowish residue that easily scrubs...