Any way to refresh white vinyl?

I don't use anything stronger than GoJo crème type hand cleaner on vinyl of any color. Strong chemicals will do the same thing to these materials as it will do to your skin.
409, Purple Power, Wesleys, will eat the stitching/thread, then covers come apart at their seams. Maybe you can rinse it enough to dilute/prevent. Good luck

Good tip on being careful with strong chemicals. When I was a kid I used 409 on the dash of my Mom's Valiant, trying to be helpful, and it removed the lettering, Oops.