I have noticed that in the recent cold weather my windscreen blades seem to be frozen in that they do not clear the screen of the screenwash. The blades totally fail to come in contact with the windscreen.
Yes, Mike, go for the Bosch aerotwin as Mick recommended, they are worth it. I'm using them too. The material of the blades deteriorates over time, even if not used. And sunlight will speed up this process. So your old ones are really old by now.