A trick that I was told by someone who works on vinyl seating and restoration was to use mineral oil (yeah, that stuff that you find in enema bottles) to maintain and revitalize vinyl. It has to do with how the mineral oil interacts with the polymers in the vinyl. I'll dig around and see if I can find more info on this, but it works great on keeping the vinyl like new.
The 303 is great for protecting from UV rays. I use both.