I’m just going to clean it an roll with it.We have had this issue on BMWs, there is a bulletin for it. The gel pad for the rain sensor can have a drip that runs down the glass. BMW, at least, says to just clean it off. I assume it’s a very similar part on the mustang.
Bumper to bumper warranty is over?
My rain sensor leaked about 10 inches down when I left the car for 6 months in the hot garage while I was gone. A month or so later it leaked again but just a tiny bit. It's been a month or so and no leaks and I tested it and it still works. My bet is that yours still works and will continue to work.
So why not have it replaced?
If it was mine, I might not let a dealer fix it for "free".
This is the part I don't get. If the gel is there for a reason (i.e. to bond the sensor optically to the glass, so that it can see water droplets), then how come losing it is not a problem?
My guess is that enough will always remain for it to be effective. Maybe? Haven't noticed this yet with my 2018. I probably just jinxed myself...
See, that’s the thing. It’s not really losing anything, besides some surface “wetness”. As long as there’s no air bubbles, it’s good to go. I’m trying to think of something similar to help describe the material, but I’m struggling with that. Manufacturers used to use a physically bonded prism to perform the same function. Those were non removable, but made out of a hard material like plastic or glass. The newer versions are replaceable, but that requires a different method to transmit light between the parts without obstruction (like air bubbles). That method is the transparent gel pad. Here check this out. Maybe it will help describe the gel some. You can see in this video when he tests if it’s cured how it’s kinda slimy, and again when he sticks it to the glass. The surface is slightly moist, and that moisture collects over time into a drop.