Thanks for the reminder about not trying 'to erase 80 years in 5 minutes'. That should be a big ol' no-brainer, but I didn't remember to put it in my post. When I got my one hundred year old Century plate camera, the bellows was filthy and so stiff I was afraid to extend it. I started with a thin coat of saddle soap with as little water as possible, let that dry a day and repeated the step. Then, over the next four days I applied four thin coats of Talas Leather Saver. All I can say is that the bellows are now gorgeous and supple without being too soft (or oily).
I'm sure there are many products and many techniques for restoring bellows. It almost certainly depends partly on what condition they are in and what exactly the construction materials are. Perhaps if we put together enough testimonials of actual bellows restorations with fairly explicit details, this thread can be a de facto data base for old bellows first aid. Camera rescue is a noble (and fun) endeavor.