I purchased a "wiper arm upgrade kit from City Racer, but when it arrived, there are NO groves inside the arm to fit over the groves in the wiper motor shaft. City Racer claims that they are supposed to be smooth and that they work great. My concern in in snow,heavy rain, or hail - when you need them the most, that the extra pressure would make them slip on the shaft. Has anyone used these? Advice?