Protect the Protective Top Coat
Plasticizers are volatile, that simply means they can and will evaporate or become a vapor at normal temperatures and atmospheric pressures. The plasticizers are added to the vinyl material and then a protective top coat is applied to the vinyl to better to lock or seal in the plasticizers. So the ideal goal in maintaining vinyl is to protect the original top coat on new vinyl and this will protect the vinyl material under it.
As the top coat is degraded or worn off, the plasticizer oils will out-gas and this will leave the vinyl hard, rigid and brittle and this is when you will see vinyl crack or fracture.
To protect the top coat you want to stick with cleaning agents that take this top coat into account, this is where we come full circle to the beginning of this article where you are recommended to use the 303 Fabric/Vinyl Convertible Top Cleaner to clean vinyl surfaces as it is specifically formulated to clean will causing no harm to the top coat.
Things to avoid getting onto vinyl are substances and solutions that can harm or degrade the top coat, this would include oils or oily products, fats, harsh detergents, and things like suntan oils on your skin in the case of things like seats, both car seats and boat seats, as well as any place skin would touch.