How to Stop the Leak from the Third Brake Light into the Boot of Mercedes SL R129

The leak into the boot from the third brake light is a typical problem on the R129 Mercedes SL. It took us a while to realise that that's the reason why water leaks from under the lid, but when we found out third brake light was to blame, we decided to fix it.

How do you know the third brake light is causing the water ingress into the boot of your R129 Mercedes SL? Well, a good indicator is if once you open the lid, water starts running down these metal rods that attach the lid to the body of the car:

Having removed the boot lid cover, as described in the previous post, and having fiddled about with the third  brake light enough to understand that there was no easy way of getting it out, we decided to take the silicone approach instead.

As our R129 is outside and exposed to the elements at all times, the silicone of choice was this:

Just to be on the safe side in case it rains unexpectedly while it's drying, we though we should go for the one that seals under water.

Another thing you need is a syringe, as the nozzle on the silicone bottle is way too big. To give you an indication of the size, here is the syringe next to the brake light. 

Pump some silicone into the syringe - no need to make it full. To make the silicone bond properly, make sure you clean the area around the third brake light of any wax. Then start to apply the silicone around the light:

Once you have gone around the third brake light with a syringe, wet your finger and smoothen the silicone strip down with your finger/fingernail. Have some wipes on hand to clean your finger as you do it and quickly wipe down any smudged silicone from the R129. If it looks like there's not enough once you smoothen it out, you might need to apply some more silicone. 

This is what the finished result looks like:

Now let it dry and then try spaying/pouring some water over the light to test how good the seal is.