Mark D wrote:

I've used Rain-X for decades on numerous vehicles. I've never had the
stuff go blotchy, or spotty as it loses its effectiveness, so what you
have on your glass is no doubt something else?

After a few months, the product is gone off the glass.

All it is, is alcohol, and water, and you can get somewhat similar
results by using straight 91% pure alcohol.

You apply it like a wax, let dry, wipe off with a clean damp towel, and
then final buff with a clean dry towel. I swear by this stuff. It's
saved my hide a couple of times. Mark

The water and alcohol are the solvent / carrier for the:

BENZENEMETHANAMINIUM,
N-[2-[(2,6-DIMETHYLPHENYL)AMINO]-2-OXOETHYL]-N,N-DIETHYL-, BENZOATE
(1%)