* Fuel injectors: These have O-rings to seal them into the fuel rail.
* Fuel pressure regulator: This may use O-rings.
* Fuel pump: The fuel pump itself has seals, some of which might be O-rings, but these are usually internal and not easily accessible.
* Fuel filter: While not typically O-rings, the fuel filter connections might use similar seals.
* Fuel lines at connection points: Some connection points *might* use O-rings, but usually rely on crush washers or other sealing methods.
If you're having a fuel leak, it's best to visually inspect the entire fuel system, paying particular attention to the areas listed above. A professional mechanic will have the proper diagrams and knowledge to pinpoint the source of the leak and the appropriate seals involved. Don't attempt fuel system repairs yourself unless you are experienced in automotive repair and have the correct safety precautions in place, as fuel is highly flammable.
