GLC Rain Light Sensor Failure

That sounds like a mess of malfunctioning sensor issues. I'm no expert, but could it be a simple fuse problem? Have you checked the fuse box diagram to see if they're all okay? I had a similar weird car electronics glitch once, and it turned out to be just a blown fuse. Seriously hoping it's an easy fix for you because that list of symptoms sounds expensive!

I appreciate the suggestion, but I did check all the relevant fuses. They're fine. Any thoughts on the likelihood of the windshield gel pad causing the malfunctioning sensor? And what kind of sensor calibration might be involved in resolving this auto sensor issue?

Okay, so fuses are good, bummer! That windshield gel pad thing... I saw something about that on a forum somewhere. I didn't really pay much attention since I didn't think it would apply to me. If you suspect it, maybe get it checked? I would probably take it to a workshop, they should have the tools to properly diagnose the car components and recalibrate everything. Sounds too complicated for me to mess with, to be honest.

It was indeed the windshield gel pad forming bubbles, causing the rain-light sensor fault. The malfunctioning sensor was triggering all those errors. Replacing the gel pad resolved the issue; total cost 62€. Everything is back to normal now.