The windshield washer stopped working - fluid wasn't coming out - and when I looked in the reservoir I couldn't see anything, so I put some Rainx in there. When this did not work, I called the dealership for an appointment, since the warranty was still active. Didn't want to go fiddling around in there on my own looking for something loose
The man at the dealership asked if I'd put any fluid in the reservoir, and I said yes. "Was it Hyundai washer fluid? Anything else will invalidate the warranty. Anything but the Hyundai formula could gum it up." I hung up. And checked the owner's manual again. It says Hyundai fluid is recommended, but nothing about "don't use anything else."
When I told them this at our regular shop, they fell around laughing. "How are they gonna know if it's Hyundai fluid in there? Do they come in different colors?" "Are you sure you didn't call the Ferrari dealership by mistake?"
Well, I stewed about this for weeks. Finally I took the car to the dealership without mentioning that I'd added any fluid. In 15 minutes they found that a tube had come out of the reservoir, put it back in and the washer has worked fine ever since.
So the moral is...actually, I'm not sure. Don't answer questions from a car dealership?