From the other car forum I frequent when I asked for a good protectant:
all products for treating the black vinyl and rubber parts on a car are a blend of glycerin, silicone, mineral oils, plus maybe some eye-of-newt, toe-of-frog etc. The main difference is in the liquid carrier, which will be either water based or solvent based. The water based carrier helps spread out the product and clean the rubber, leaving the glycerin etc on the surface of the rubber looking nice and glossy. As it is not actually bonded to the rubber it will dissipate after a short while, leaving the rubber cleaner, but back to its natural state. The solvents in the solvent based carrier products penetrate into the rubber opening up pores that allow the glycerin etc to sink in and stay in place longer. BUT, this is like crack-cocaine because these solvents break down and dry out the vinyl and rubber leaving them shabby looking when the glycerin etc evaporate. You reapply more product to regain the black luster, but the solvents open up and crack the rubber more. This becomes your life on drugs! Read the label or look up the product fact sheet and stick with the water-based products.
Someone also mentioned Mequiar's Vinyl and Rubber Cleaner 40, and Aerospace 303. I haven't tried either yet. I have Slick's Trim Cleaner and it's water-based. It's good, but it doesn't take out wax residue like some of the others I've used(Autoglym HD wax left some nastiness where I didn't protect good enough)