Discolored or broken vinyl trim parts (even if some morsels are missing between the broken parts) can be perfectly repaired using Araldite (or similar) two component epoxy adhesive resins (choose the fast-setting version). The customary plastic packaging used in great volumes today (with paper background and the product shrink wrapped) can be used in the process. Cut out the bigger flat parts of such plastic wrappers. Araldite does not glue to them: even if it seems that it does, it can be easily snapped off once the resin is completely hardened.
Avoid silicone spray. Many trim areas—especially parts of the dashboard exposed to direct sunlight—are constantly bombarded by ultraviolet rays which break down the molecules comprising the vynil skin, allowing raw vynil molecules to escape the panel.