Genuine Nissan RB20/25/26 Rear Cam Plug / Seal Half Moons
These are a must replace when you remove the valve cover. They become hard and dry over time being soaked in oil and heat cycled. They lose their "squish" eventually and don't seal oil anymore. The oil leaks down the rear and sides of your engine and makes a mess that is hard to clean. They're very reasonably priced, so do the job correctly and replace them when doing valve covers.
Sold as a set of two