What Ronkh said plus I clean with IPA and my favorite is Griot's Garage Rubber Cleaner
but I also like gummi fledge ...
Use the GG Rubber Prep, a much better product. After cleaning use UTTG for a coating. Never understood the raves about 303, a mediocre product at best. Sanding? No way!
EDIT: Should have read Accumulators post first. He da Man!