Several old timers told me that they leaked when the trucks were new, just not a very weather-proof design. Mine leaks some at the top, but primarily at the lower outside corners. Water will blow through when driving.
What do I do? I carry some paper towels with me, roll one up and close the windshield against it in both corners. Doesn't completely stop the leak, but helps a lot.
That said, the only time I'm out in the rain in it is if I get stuck with a change of weather. I'd rather drive it when it's more pleasant out.
David Bush