I replaced the hose as a precaution against future failure, I had the trunk stripped so i took the opportunity to do it while it was easy to access.

If I had to do this again or had to do the door air lines, I would not bother to replace all the hose, I would replace the just the broken length of hose and splice it into the old hose with a hose with an inside diameter the same as the outside diameter of the hose (5 mm). The splices should fall in an area that is not flexed when opening the hatch or doors. The hose is mostly inside the wiring loom and stays in the car anyway.

Remove the upper and lower right hand side panels in the trunk. Have some spare fasteners for the upper panels, I removed all five trunk panels as well as the two hatch liners and broke most of the fasteners on one upper panel and none on the other upper panel, you just have to pull them out square to the panel surface at the fastener. These are the replacements. CLICK Mercedes part #A003 988 41 78
Remove the two liners on the inside of the hatch by removing the screw under the plug in the hand hold on the lower hatch liner, remove the two screws that hold on the upper liner on the hatch. Use a plastic trim tool to pry them out of the retaining clips.

Remove the latch body from the hatch, there are seven star head screws (#30) and four nuts (10mm) holding it in place. Remove the electrical connector for the trunk latched signal and slit the hose on the 'L' hose connector with a razor blade to prevent the risk of breaking the connector, then you should just cut this old hose as far back as you can see it.
The air line to the trunk lock passes through the right hand rubber conduit that is connected between the hatch and the car body. The yellow airline is visible in the photo. The conduit assembly consists of three parts, the rubber conduit itself and two plastic collars that snap into each end of the conduit they cannot be seen normally, it is these collars that keep the conduit in place. When these collars are in place in the conduit a lip on the conduit forms a seal against the car body or hatch.


These collars are a pain to take out of their holes in the body but there is a trick to get them out. Gently pull the rubber away from the collar that fits in the hole in the body or hatch. There is a collar at each end of the conduit and each plastic collar has four tabs on it, one on each side. The tab ends are slightly above the metal surface when the collar is pulled up as far as it will come and are thus accessible to be pushed inward. Push in the tab on one end and lift the collar partially out of the hole, then push in the tab on one side. This enables you to remove the collar from the hole. You can see the tabs in the collar in the photo. I used a sharp scribers with a right angled bends in the ends. The collars must be removed from their holes as they have to be reinserted into the rubber conduit before replacement as they provide the pressure to seal the joint.
I cut the hose as close to the hatch as possible,and on the inside of the trunk I dropped the rear of the roof liner an cut and unwound the black tape 4" from the hole in the steel and cut the air line 4" from the steel, I grabbed the air line with pliers and pulled the air line free.

The new airline has then to be threaded through the collars and the rubber conduit. Push the new airline through from inside the trunk through the first collar and pull out a couple of feet of the airline, put some Vaseline or something similar into the opening on the conduit and push the airline end through it and the collar. With the Vaseline the line slid through the rubber conduit like grass through a goose, poke the end of the airline through the hole in the hatch and toward the opening where the wires exit. Pull the extra line through sufficiently to reach the latch on the hatch. The latch will need to be removed to get to the airline connector. If you have too little or too much airline to attach the airline can be pulled through to take up the slack or add more airline as needed.

Make sure that the collars are securely inside the ends of the rubber conduit and snap them back into place, the rubber seals out the rain water, you can hear the four snaps as they click into the locked position. Gently tug on the conduit to make sure they are locked down and sealing properly.

Tuck the airline into the side of the hatch window with the old airline and wiring, use the clips if you can.


Thread the airline into the hatch body and toward the adapter on the hatch locking mechanism. Attach the hatch wiring adapter and the air line to the lock. I warmed the end of the air line to make it easier to push the line onto the connector, no need to snap the airline connector now.



With the the wire and airline in place on the lock it is bolted back into position in the hatch.



The other end of the line is then warmed and pushed onto the TEE connector attached to the passenger door lock air line.
In the following photo you can see the CLP/SSM in the trunk well inside its foam cover, it is completely surrounded by the foam on all six sides, it sits on its side and rests on a foam block above the trunk bottom. The whole assembly is then wedged under the frame of the car to keep it in place. This puts the pump about 2" above the bottom of the trunk, I had always thought it sat on the bottom of the trunk. Now put back the trunk trim and the job is done.

There are some extra wires in the above photo, they are for the extra trunk light on the passenger side and the reversing camera.

 

Hi Dave, hadn't you replaced this hose once before? I thought I had read in a (long ago) thread that you replaced or repaired this rear hatch hose. Just wondering.. Great post for those who are having trouble with this leak!

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I have never done this before and I am doing it now as preventative maintenance. I might as well do it as the trunk was taken apart to wire up the rear view camera. There are many posts where the air line that passes through the rubber conduit at the top of the hatch breaks from being bent each time the hatch is opened. I doubt mine was near to breaking but I thought I would fix it anyway. I am replacing it with a polyurethane air line, a guy in a previous post said what we have now is not the correct material. The line must get pretty stiff in the cold weather and that would lead to weaknesses in the line.
I am having trouble refitting the roof panel, so I regret doing this proactive fix. If you have not got a broken airline do not bother to install a new line.