Whats wrong with new 21 year old calipers ?   I don't think oil/nut buster will help as oil will cause the rubber goodies inside to swell up and make things worst. I have freed up a few but it wasn't worth it in the long run. If you do get it apart somehow, you will have to replace everything inside anyway so why not just bite the bullet and spring for a set of re-built one. It takes all kinds of tricks to free up these things.  Maybe someone out there may has learned  some new ways by now .  Good luck

Way to go Dude. Hope the other one is that easy.  New kits and you are on the way. There are more ways to choke horse than feeding it ice cream