Syl-glide. I bought a bunch of it at a auto parts store years ago. We used it to help rubber o-rings slide into place -- as well as to put it around window seals to swell them a bit -- which helped with minor squeaks and air leaks. It comes in a tube that looks a little bit like a big tube of toothpaste, or those squeeze tubes you squirt lower end fluid into an outboard with. Squeeze it onto a rag and work it into the tire. If you lay it on too thick it will have a slightly blue tint. Leave it sit for a week or so and then wipe it off with a lint free towel. Looks a lot like Armorall when done, but lasts longer. Only drawback is that because it stays "wet" for a pretty long time it can get on your clothes or whatever rubs against it. If the rubber is really deteriorated you will find that when you rub that first application off your towel will be black or grey. Apply another coat, let it sit a week, and do it again until the time when it does not come back dark...should leave a nice gloss on tire and preserve it well.
Some use silicone in a spray as well...but this will not last as long and for whatever reason tends to dry crack on the rubber over time.
Always good to see folks preserving the originals!