John in VA wrote I've used RainX for 40+ years without issues - the "real" stuff, not the windshield/glass cleaner, following the instructions.
Same here, although I've only been using it for ~35 years! I just reapplied it to my cars earlier this week. I find it lasts up to 2-3 months on the windshield depending on the amount of rain the car sees (far longer on the side and back windows), and most of my cars are parked outside. When I pick up rental cars for road trips, they get a coating as well. And I've even taken a small bottle of RainX to Europe for use on those rental cars.
Application process is easy: (1) clean and dry windows using any method (paper towels, newspaper, Mr. Clean Magic Eraser), (2) apply RainX with a clean, dry paper towel; I usually apply it twice to make sure I didn't miss any areas, (3) get a couple paper towels wet and wipe the entire window with them, and (4) dry the window with more paper towels.
I used to avoid the very top-center of the windshield where the rain sensor is, but all the newer sensors do a better job so I just apply RainX directly over them now.
Definitely avoid the RainX product you add to the windshield wiper fluid - I've heard nothing good about that stuff.
(although if you apply Rain X every week it works awesome!!!)
