Mercedes W123 Seals Guide: Door Weatherstrips, Window Rubber & Sunroof Seal

On a Mercedes W123, old rubber shows up in a few familiar ways: wind noise from the door tops at speed, a damp footwell after rain, water marks under the sunroof, or a trunk floor that never quite dries. The car is built to last, but its rubber is forty years old or more, and hard, cracked seals let in the water that starts rust.

This guide goes through the W123 seals one by one: what each seal does, how a worn one shows itself, and which of our parts and sets cover it. It applies to the W123 sedan, and we note where the C123 coupé and the S123 wagon (estate) need different parts.

Find the Leak Before You Buy

Before ordering, it pays to know which seal has failed. Two simple checks find most problems.

The paper test. Close a door on a strip of paper and pull it out. If it slides out with no drag, the seal is not touching the body at that spot. Work your way around each door.

The hose test. With someone inside the car, run a garden hose slowly over one area at a time: windshield, door tops, sunroof, rear window, trunk lid. Start low and work upward, so you know which seal the water came through.

Leave the car a day after rain and check the footwells, the carpet under the rear seat and the spare wheel well. Where the water collects tells you a lot about where it got in.

W123 Door Seals (Weatherstrips)

Each door has a large rubber loop seal shaped to its outline. When it goes hard or flat, you get wind noise at speed, water on the sills and doors that slam with a hollow sound. Sedan door seals come as a set of four, one for each door.

Door seals only. The W123 door seal set lists OEM references 1237201578, 1237201678, 1237300178 and 1237300278 for the front and rear doors.

Doors plus trunk. The 5-piece door and trunk set adds the trunk lid seal to the four door seals.

The model names in some titles, such as 200, 220, 230, 220D and 240D, refer to sedans. These are body seals, not engine parts, so the engine your sedan has makes no difference.

Window Seals: Scrapers and Run Channels

Two smaller seals work with each door window, and they are often the real cause of a whistle or a slow window.

Belt scrapers. These are the strips along the bottom edge of each window on the outside of the door, sometimes called beltline seals. They wipe the glass as it goes down and keep rain out of the door. When the felt wears away and the rubber cracks, water runs into the door, and a door full of water rusts from the bottom. The set of four outer scrapers is for the sedan. It is one of our most-ordered W123 parts.

Run channels. The run channel is the rubber channel in the door frame that the glass slides in. A worn one lets the glass rattle and lets wind past the top of the window. A swollen or torn one makes the window slow and can strain the regulator. Run channels are sold in our sedan sets below.

Windshield and Rear Window Seals

The W123's front and rear glass sit in rubber seals that also hold the chrome trim. When these seals shrink and crack, water gets under them and sits against the metal of the window frame. Rust around the front and rear screens is a known W123 problem, and it nearly always starts with an old seal.

Signs to look for are bubbled paint near the glass, water in the front footwells (front screen) or water in the trunk and on the rear parcel shelf (rear screen).

We sell the seals one at a time, as the front windscreen seal and the rear windscreen seal (OEM 1236700239), or as a front and rear pair.

Replacing a screen seal means taking the glass out. Most owners have a glass fitter do this. If you are restoring the car, the best time is when the glass is already out for paint or rust repair, so the frame can be fixed and painted before the new seal goes in.

W123 Sunroof Seal

Many W123s have a steel sliding sunroof, opened with a crank or electrically. The rubber around the panel shrinks with age, and then water drips onto the headliner or the seats.

The W123 sunroof seal repair kit has four pieces, shown together in the listing photos.

One thing to check first: many sunroof leaks are not the seal at all. The sunroof tray has drain tubes at its corners, and when they block, the tray overflows into the car. Pour a little water into the tray with the roof open. If it doesn't drain away quickly, clear the drains before you change the seal.

If the crank handle is broken, there is a chrome sunroof crank handle (1237800016) for manual sunroofs.

Trunk Lid Seal

A wet spare wheel well or a damp trunk mat usually means the trunk seal, though it can also be the rear screen seal. The sedan's trunk lid seal lists OEM 1237580098. Check the channel it sits in for rust while the old seal is off, and clean it before the new seal goes on.

Bumper Rubber

The rubber strips on the bumpers don't seal anything, but they fade and crack along with the rest. We list the front bumper rubber pair and the rear bumper rubber, both for the sedan and coupé.

Complete W123 Seal Sets

If the car still has its original rubber, buying one set is easier than ordering part by part. Here is what each set contains, from smallest to largest. All of these are for the sedan.

Doors and run channels. The door weatherstrip and run channel set covers the four door seals and the window run channels.

Doors, scrapers and run channels. The door weatherstrip, scraper and run channel set adds the four outer scrapers.

Doors, scrapers, run channels and sunroof. The same set with the sunroof kit, for cars with a sunroof.

13 pieces. The 13-piece set shows four door seals, the trunk lid seal, four outer scrapers and four run channels.

Windows and sunroof. The window and sunroof set has the front and rear screen seals, the 4-piece sunroof kit and the four outer scrapers. It suits a car whose door seals are still good.

Screens, doors and windows. The screen, door and window set has the front and rear screen seals, door seals, run channels and scrapers.

14 pieces. The 14-piece set lists four door seals, the trunk seal, the front and rear screen seals, the three bumper rubbers and four outer scrapers.

Everything. The complete rubber seal set covers doors, trunk, screens, bumpers, sunroof and windows in one order. For a full restoration, the four-door full rubber and trim set pairs the seals of the 14-piece set with the side and rocker trim strips shown in its listing photo.

Coupé (C123) and Wagon (S123) Seals

The coupé has no B-pillar and its side windows have no frames, so many of its seals differ from the sedan's. For the coupé we list the 2-piece outer window scraper set.

The wagon's rear doors differ from the sedan's. For the wagon we list the 4-piece run channel set and the outer scraper set.

For other coupé or wagon seals, send us your model and year and we'll tell you whether a sedan part fits.

Fitting Tips

Let the rubber relax. New seals come folded in a box. Leave them out at room temperature for a day, or in the sun for an hour, so they lose the kinks before fitting.

Note how the old seal comes off. Look at how it is held and where its ends meet before you pull it, and fit the new seal the same way.

Clean the flange. Scrape off old rubber and adhesive, treat any rust you find and let it dry before the new seal goes on.

Doors may feel stiff at first. New door seals are thicker than the flattened old ones, so the doors can be hard to shut for a few weeks. Give the seals time to settle before adjusting the door strikers.

Frequently Asked Questions

How do I know if my W123 door seals need replacing?

Wind noise from the door tops, water on the sills and a paper strip that slides out of a closed door without drag are the usual signs. Seals that are hard, cracked or flattened should be replaced.

Is a W123 sunroof leak always the seal?

No. Blocked drain tubes are a common cause. Pour some water into the open sunroof tray. If it drains quickly, the drains are fine and the seal is the likely cause.

Do the seals fit every W123 sedan, from the 200 to the 300D?

Yes. The seals belong to the body, not the engine, so a sedan seal fits any W123 sedan. Titles that list 200, 220, 230, 220D and 240D are sedan parts.

Do sedan seals fit the coupé or the wagon?

Many do not. The coupé has frameless windows, and the wagon's rear doors and tailgate are different. We list coupé scrapers and wagon run channels and scrapers separately. Ask us before ordering other seals for these cars.

Should I buy a complete set or single seals?

If the car still has its original rubber, a set costs less than the same parts bought one by one and fixes every leak in one job. If only one area leaks, buy that seal. The window and sunroof set suits cars whose door seals are still good.

Browse Mercedes W123 Seals

All of the seals in this guide are in our Mercedes W123 collection, and more parts for classic Mercedes models are in Classic Mercedes Parts. If you are restoring the inside of the car as well, see our W123 interior restoration checklist and the classic Mercedes grill and chrome trim guide. Not sure which seal fits your car? Send us your model, body style and year and we'll confirm before you order.