Don't use window washer fluid for cars, had a customer that cleaned his car with it(!?) before applying his decals (yes, yes, he saved a couple bucks to do-it-himself). The decals peeled about 2-3 hours later, and of course he asked for replacement. This was the first time I had any failure with the material at all, so you can tell I was surprised. Luckily he admitted using window washing fluid, otherwise I'd be stumped why they would fall off. Didn't think about ammonia, but it could be that the fluid contains that. Thanks for the tip, Fred!
We use citrus based surface cleaner ment for cleaning before applying decals, doesn't cost much, already pre-mixed and smells good.