Just to clarify the Armorall issues mentioned several times above:
The reason you find armorall, and similar "rejeuvenators" seem to lead to cracking, and/or once you start using them, you have to keep using them, etc..is that they work by migrating the plasticizers to the surface. This means drawing plasticizers from deeper down, up to the material's surface.
As you deplete the surface plasticizers, and progressively deplete the deeper plasticizers, the material (Which needs the plasticizers in the formula to provide plasticity/flexibility, etc...) becomes progressively more brittle...hence, cracks more easily, etc.
When you start using it, the added surface plasticity, etc makes the finish look shinier and newer...but, its like licking your lips when they feel dry....eventually, they get chapped.