during a Christmas trip from Boston to Cincinnati - as the temperature got progressively colder the wipers slowed down. As the weather warmed during the week the wiper function returned to normal. I also think the windshield got quite a bit of salt spray on it, which increased the drag on the wiper motor, exacerbating the problem. It is probably time to relube that mechanism (which I have never done). Maybe you could, as a temporary measure, spray some WD40 on the wiper transmission?

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Chip Johnson