Okay, I had to try this myself after I heard/seen it but a friend of mine had an old Chevy pickup and the dash was faded brittle and had some cracks. He said he was going to use Vaseline as Armour-All didn't treat the vinyl with the softeners it needed to bring it back to original. We'll I'll be damned if it didn't work! It took a couple applications to bring back the pliability but it was in pretty bad shape. He said his dad turned him on to it years ago. Works on wiper blades, vinyl, plastics and the rubber seals around doors and windows. The downside is it isn't pretty and shiny like Armour-all but I really done car about the shiny part.
Best way to use it is on a nice hot day, give it a coat with your fingers or from a rag, let it set for a couple hours and wipe of the excess. Repeat as needed. Works really well on wiper blades that get stiff and clean well one direction but don't the other.
Much cheaper than any vinyl protectant on the shelf too.