Mercedes E320 Remote central locking fix

If your remote central locking doesn't work, you may be able to fix it for free!
The most common problem seems to be a non-working key, and then sometimes Fuse 8 is blown. And then there is a problem with the antenna amplifier, which as well as amplifying radio signals from the rear side screens, also acts as a radio receiver for the long-distance action of the key.
But it seems a fault in the wiring loom is quite a common problem too. Mercedes split the supply wire to the aerial amplifier into two wires, inside the wiring loom. For some reason, perhaps due to left over flux, the wire corrodes and the joint fails.
This video shows how to diagnose the problem, and how to fix it.