I was especially keen to do this on my 300SE as water would get into the passengers foot well in the rain.   This would only happen when the car was parked nose up on an incline.   My theory was that debris may have been preventing this area from draining properly.

This job can be done in about two hours, even assuming a lot of cleaning time.   It is certainly worth doing on any W126.     As covered previously, the first step is to remove the wiper arms.   The little plastic covers flip up and the 13mm nut is behind.   The arms will only come off if they are raised.

The drain covers are next. At least on right hand drive cars, the cover is in two pieces. There is a plastic fastener that holds the two pieces together that is just pulled out. The top seal is available for purchase, and these are often in poor shape after 20 years. The picture below shows the edge of the seal on my 300SE. The middle wasn’t quite as bad.

The lower seal is generally in much better shape as its covered by the bonnet. I was not able to find a replacement for this, but could re-use both of my seals. Once the seals are off, there are metal clips that hold the cowl drain covers to the firewall. Once those clips are removed, the drain covers can be gently lifted up. The metal clips hold it to the outer firewall and the covers have molded edges to clip in under the windscreen. I found an old toothbrush to be useful to clean the mesh part of the covers.

Unlike the 560SEC, which had debris from leaves in the cowl area, the 300SE had fairly thick dirt. No rust had started that I could see. The drain holes were open, but the thick dirt may have prevented the water getting to the drains in all circumstances. I’m hoping this cleaning of the 300SE cowl drains will stop water getting into the cabin and prevent rust.

I’m not sure what it is fore, but there was a wiring harness that looked factory coming through the firewall into the cowl drain area.   Instead of being plugged into anything, it had just been taped up.   Please post in the comments section if you know what this is for.

I was actually expecting more debris and some blockages here, so I guess it is possible that something like the windscreen seal is also leaking.   It’s certainly a lot cleaner than it was.

Once cleaned, its quite easy to replace the covers and the two seals. I used my new upper seal and the new wiper shaft seals.

This is the sort of job that is good to do at home as it would be expensive to get a mechanical to properly clean out this area.   Removing these covers really is very simple and the whole job takes about two hours, taking your time.   Having owned this car four years, I really should have done it sooner.

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Before I did so, I had some new parts to install.   The first were the rubber boots that cover the windscreen wiper shafts.  On most W126 cars they are almost non existent.  On my 560SEC, I had the remains of one, and the other was completely gone.    The picture below shows the two new boots along with the remains of what was left on my car.

Second was the rubber seal that goes between the W126 Cowl covers and the windscreen.  These are normally cracked and perished.  The seal on my SEC wasn’t too bad, but it was covered with hairline cracks and no longer sitting flush against the glass as it had gone hard.   These are now available as reproduction parts.   I also purchased one for the 300SE and 560SEL as the postage was going to be about the cost of the seal if I only purchased one.

It is hard to see from the photo, but the one on the top is the new seal.   The old seal has many cracks as shown.

The W126 cowl covers go on fairly easily.   I found it easier to put on the bigger one first, starting with the windscreen side to tuck it under the glass.   The seal shown above is just pushed onto the plastic cowl cover once it is in place.   The windscreen wiper seals just slip over the wiper shafts.

There are supposed to be five clips holding the covers on to the inner firewall, but for some reason I only have two.  I forgot to order 3 more in my parts order.   I couldn’t find a new seal for the inner firewall, so I just re-used the original one.   It wasn’t too bad.

The windscreen wiper just go on in the reverse of how they are installed.   I made some marks on the windscreen before I removed them to align.  This can be seen in the photo above.   I have not yet tested the wipers, but I am confident they are in the right position.

My final parts for the cooling system should arrive next week so I should be able to put the car together and test all the work I have been doing.

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In order to remove the W126 cowl drains cover, the seals at the firewall and windscreen must first be removed.   In the photo above, I have removed the seal on the firewall but not the windscreen.   Once I removed the firewall seal I noticed that some light rust had started at the top of the firewall.   Both of these seals just slide off.

Next step is to remove the wipers.   As can be seen in the photo above, the end caps push up to reveal the nuts that old them onto the splined shafts.    Once the nuts are removed, the wiper arms must be in the upright position to remove them from the splined shafts.

Once I got the W126 cowl drains cover off, I was pleasantly surprised withe the condition the drain area.   Other than the  surface rust in the first photo the area is completely rust free.   All I needed to do was vacuum out some of the larger debris and use some rags to remove the smaller dirt.

Next step was to remove the surface rust on the firewall.    I started using a wire wheel on my drill to prepare the metal for some rust guard paint.   The wire wheel creates a lot of small dust so it is important to protect sensitive areas with some rags.

Once the loose rust was removed I painted some rust guard on the affected areas.    This should stop the rust that is already there and prevent it from spreading further.

The rust guard paint is black vs the original Nautical Blue.  Luckily I still had some of the touch up paint from when I fixed the stone chips.   I used some of that paint to cover the black rust guard.   This area will be covered by the seal, but it is supposed to be body coloured and I had the paint on hand.

The car is now ready for the W126 cowl drains cover to be re-installed.  Before I can do it, I am waiting on a few parts to be delivered. This includes a new seal for near the windscreen and the rubber seals that go around the windscreen wiper shafts.

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