I'am using Oracal 751 Cast (with GXP-775 application paper) for years and never had promblems that stickers come off from the window, even with high pressure and whipers.
But some customers sometimes complain that their sticker comes off from itself. So I wonder if the customer did'nt follow my install-description or if they really have the problem !?
I thougt it can be a kind of wax/polish from the car-wash that's on the window or something like that. Or a product that's in the window washer nozzles like antifreeze.
It's strange.