As is the case with any rubber parts on your approximately 30 year old car the fuel filler neck seal on your W123 may not be functioning as it should be. If you use alternative fuels this can be exacerbated by the fuel's reaction when it contacts the rubber. Change it today before you get water, fuel, or dirt in to your trunk through this opening.



  1. Mercedes W123 Fuel Filler Neck Seal Replacement, Fuel Filler Neck Seal: step 1, image 1 of 1
    • When inspecting your fuel filler neck seal look for dryness, brittleness, or like on this particular diesel W123 obvious damage. This was caused by drips of B99 biodiesel on the already aged rubber seal.

  2. Mercedes W123 Fuel Filler Neck Seal Replacement: step 2, image 1 of 1
    • Gently pry around the edge of the old seal with a flat blade screwdriver or a large plastic spudger type tool. The old seals often stick slightly to the car.

  3. Mercedes W123 Fuel Filler Neck Seal Replacement: step 3, image 1 of 1
    • Pull the seal off of the fuel filler neck. It will look like this once the seal is off.

  4. Mercedes W123 Fuel Filler Neck Seal Replacement: step 4, image 1 of 2 Mercedes W123 Fuel Filler Neck Seal Replacement: step 4, image 2 of 2
    • Use your thumb to press the new seal in around the filler neck. The new seal has a lip on the back that must be pressed in to the hole around the neck. This lip will grip the metal edge of the hole for a tight seal.

  5. Mercedes W123 Fuel Filler Neck Seal Replacement: step 5, image 1 of 1
    • Here's one last look at the damage done by the biodiesel. The owner of this W123 will be more careful in the future not to drip fuel on the filler neck seal when filling with B99; at that concentration, biodiesel is very caustic to rubber. Lesson learned!


Once finished, consider covering the rubber seal in a light coating of silicone grease to help preserve it.


Nicolas Siemsen


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