All sorted now but I thought I'd update the thread in case someone else has the same issue. The following may help...
Upon removing the fuse box (BCM) cover and the kick panel next to it, I could see that there had been some water ingress at some point (probably through a dodgy door / window /...
I have a problem where our vehicle (2016 S550 GT Premium 5.0) has stopped responding to the key fobs.
It starts when a fob is placed in the cup holder but we can't lock / unlock the doors or start the car with the key in any other location.
I originally thought it might be a faulty RTM but I...