I would try a goof off type product, although I don't know why mineral spirits would be a problem. I would be concerned about residue with WD-40.
On word of caution, do NOT use ANY detergent type of cleaner on the slide toppers. I had a customer who, after telling her that, used Woolite thinking is was "mild," on her vinyl spa cover. The cover failed in just over a year. The wrong cleaner on slide toppers is what causes premature yellowing, cracking and peeling. I only use vinyl cleaner on any soft vinyl/plastic products.
2007 Limited SE 40fdts
Las Vegas, NV