I was putting too many miles on my 2005 SL so I bought a second car for my daily drive. And, I was also spending more than I wanted on cartage for some items I'd bought so I wanted something with some carrying capacity but not a truck or a van. After a lot of searching I found a suitably priced 2007 GL320CDI on an auction site, which I bought for a reasonable price. There are a few things wrong with it but nothing that affects it's main function, an alternative car with carrying capacity.

An example of the faults is the subject of this post. For no reason I could fathom, all of the COMAND system buttons and controls stopped responding even though the satnav screen still displayed where I was and the radio was still playing. I couldn't enter new destinations, change radio stations or swap to a different screen. All the controls on the head unit were unresponsive but the steering wheel volume worked. I suspected a fuse and found a suitable fuse diagram at FuseAndRelay.com (https://fuseandrelay.com/mercedes/ml-gl-164.html). The following YouTube post was also helpful in locating the two COMAND fuses.
The two fuses associated with the COMAND unit are the 10 and 15 amp fuses, shown above at positions 23 & 25, found at the rear of the luggage compartment. Upon inspection neither was blown and when re-seated firmly the controls started to respond again.

This is an easy fix if anyone has a similar problem and I recommend the YouTube video for location of all the fuses and relays in the W164 & X164.