I put a tshirt over it when i leave the car to prevent sun damage.
I try not to use any kind of chemical/conditioner on it...

 

Leather Cleaner and conditioner ftw....

Make sure you wipe it off when you're done, or your wheel will slip out of your hand.... lol.

 

In my M3, I use Mr Clean eraser. It is abrasive so be careful on how you use it. I like it because it turns it matte instead of shiny

Otherwise, any leather cleaner then conditioner.

 

good quality leather and vinyl preservatives have sunscreen in them...
you should protect the leather part with leather preservative and the vinyl part with a vinyl protectant.
forget the rag over the wheel (btw, what do you use over the rest of the interior??)
a convertible needs sunscreen products even more than top up cars-