After it was banned by the greenies we used to use RAINEX bought at car shops. Before engine start you would open the pilots window and leaning out as far as possible rub the RAINEX on a piece of cloth on the window. It was better than the manufacturer supplied rain repellent and lasted longer. We carried a spare bottle in our nav bags.
Yes it is a pity that such a proactive approach would end in your dismissal these days. There are at least 2 incidents on the ATSB file where forward visibility in the 737 in rain has been an issue