Agreed, some cars are notoriously picky. The wife's Golf insists on a particular expensive grade of screenwash, or its cunningly fan-shaped nozzles get coked up. Best screenwash I know is Lidl's finest W5, which is German spec, and they know a thing two about winters out on the Polish border where I used to live. Apparently it keeps the nozzles clean. Anyway, it always sells out pretty fast when it comes into the stores, so it's worth keeping an eye out for. It's bright blue, in 2.5 litre bottles.