When Nissan moved the rear fresh air vents in the deck lid forward, the holes that the original ducts went through were left in place as an access port of sorts. They used this rubber plug to seal the holes and prevent exhaust fumes from entering the car. Over time, the thin rubber in the center of the plug tends to dry out, crack, and eventually fall apart, allowing those dangerous fumes to enter the car once again. If you notice the smell of exhaust while you are driving, this is the first piece we recommend inspecting, since it is the easiest to replace. Sold individually, 2 required per car.
70 and early 71 models with rear deck grills did not originally use this plug. Instead, the fresh air vents in the rear deck lid (the holes that the grills cover) had ducting that was routed through the holes at the base of the deck. Nissan found that having vents on the deck lid would also pull in exhaust fumes, which is one of the reasons they moved the vents forward in 71. This plug can be used on 70 and 71 models to help reduce exhaust fumes inside your car if you remove the original ducting.