As an old timer I have always used a product called D&L hand cleaner, it contains lanolin for your hands but does wonders for your vinyl. It will not only clean and remove stubborn stains but will leave the material soft and pliable. In the old days us car guys used it to clean and protect our vinyl roofs on our cars, but always have used it for interior vinyl as well. Lots of good products out there but watch the chemicals... they clean but can leave the vinyl hard and it can crack. The D&L is a safe sure bet, the car collectors from yester year still use it.