Bob,
Use a leather cleaner, then a leather conditioner on the wheel. Then use a vinyl/plastic/rubber cleaner-conditioner on the center.
DON'T mix the two - Armor All or other vinyl/plastic/rubber cleaner-conditioners will quickly ruin the leather.
I use Lexol on leather and 303 Areospace on everything else. I've found ProtectAll wash to be great for interiors. Just mix up a small bucket and use a rag and rinse often. Usually don't even need the 303 inside when I use the ProtectAll wash. Dries streak free and everything looks new.