If you remove the FM reroute from your engine, you're basically guaranteed to need a new gasket. Be prepared with the right one. You could use a generic Miata thermostat gasket and trim it to fit, but why bother when you can simply stick this one on? Die-cut to the perfect shape and adhesive-backed, it doesn't get much easier than this. These are now included with current kits. 

Need to replace the thermostat as well? Get the complete kit below.