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  3. Replacing the sill seal on a Mercedes W123 | Instructions

Replacing the sill seal on a Mercedes W123 / C123

Installation instructions for sedan, station wagon & coupé

The sill seal on the Mercedes W123 and C123 Coupé is a typical wear part.
Over time, UV radiation, aging, and weathering cause the original rubber profiles to deteriorate:

  • brittle

  • cracked

  • shrunken

  • leaking

In this guide, we show you step by step how to professionally replace the sill sealing profile .

You can find suitable sill seals here:
Mercedes W123 / C123 Coupé

Scope of delivery

Included in the delivery:

When you order a set you will receive:

  • 1x driver's side

  • 1x passenger side
    (both identical)

Required tools

  • Cutter knife

  • Plastic or wooden wedge (no screwdriver!)

  • Profile rubber adhesive or bodywork adhesive

  • Angle grinder or sandpaper

  • 3–4 one-handed clamps

  • Wooden slat (approx. 2 m)

⚠ Do not use metal levers – damage to paint and chrome is likely.

Check the condition of the old seal

It is recommended to take photos before disassembly.

Typical damage:

  • cracks

  • porosity

  • Shrinkage due to solar radiation

Dismantling the old sealing strip

Step 1 – Remove sealing strip (D2)

  • Open door

  • Use a plastic wedge to wedge between the sill and the trim strip.

  • Pry it out bit by bit from back to front.

Step 2 – Remove end caps

Remove the plastic end caps ( W123 Coupe & W123 Limousine/Estate ) at the ends of the sill trim.
Often these are brittle or already damaged.

Step 3 – Remove the old rubber profile

  • Cut with a cutter

  • Peel the rubber off the stainless steel strip

  • Sand off any remaining residue.

Goal: to achieve the smoothest possible surface

Cleaning & Preparation

The stainless steel strip must:

  • fat-free

  • silicone-free

  • clean

be.

This is the only way to ensure the adhesive bonds permanently.

Installation of the new sill seal

Bonding of profile and stainless steel strip

The new rubber profile is slightly longer than the stainless steel strip – that's correct.

Procedure:

  1. Lay both parts side by side

  2. Apply body adhesive

  3. Join profile and strip

  4. Secure with a wooden slat and clamps

Tip: Work with two people.

Installation on the vehicle

After complete hardening:

  1. Insert end caps

  2. Use new mounting clips

  3. Position the strip correctly

  4. Press evenly until clips click into place.

Why the exchange makes sense

A new sill seal ensures:

  • improved moisture protection

  • less wind noise

  • clean look

  • long-term value retention

Especially on the Mercedes W123 / C123, the sill trim is a visible detail – new seals immediately improve the overall appearance.

You can find suitable seals here:
https://www.wdb-teile.de